I'm an MBA.
Fields medal 2018

Anyone else thinking the system is unfair? You have to be under 40 in the year of the award, held every 4 years  so for some people their last chance to win it is when they are 36, while some others it's 39. Sure, this kind of big contributions are most likely done at an earlier age, but 3 years does sound like a big disadvantage.
Most winners of Fields medals won it for their achievement at a young age, before 35. There were few (if any) cases of a mathematician who had not done much before 36, then suddenly made a big splash and won Fields at (say) 39. So, the disadvantage you spoke of is not that big.
Most (90%) of top mathematicians showed their extraordinary talent at a young age. Harvard math department literally does not hire tenure track APs. The reason is that anyone who needs to go through tenure track is not good enough. Instead, Harvard directly pick young top talents in their 20s and early 30s and appoint them full professors. That's how the world of pure math works. VHRM or nothing.

That's bulls**t. There are plenty of superstar mathematicians in lower ranked departments and in other countries. You are fool.
Anyone else thinking the system is unfair? You have to be under 40 in the year of the award, held every 4 years  so for some people their last chance to win it is when they are 36, while some others it's 39. Sure, this kind of big contributions are most likely done at an earlier age, but 3 years does sound like a big disadvantage.
Most winners of Fields medals won it for their achievement at a young age, before 35. There were few (if any) cases of a mathematician who had not done much before 36, then suddenly made a big splash and won Fields at (say) 39. So, the disadvantage you spoke of is not that big.
Most (90%) of top mathematicians showed their extraordinary talent at a young age. Harvard math department literally does not hire tenure track APs. The reason is that anyone who needs to go through tenure track is not good enough. Instead, Harvard directly pick young top talents in their 20s and early 30s and appoint them full professors. That's how the world of pure math works. VHRM or nothing. 
The 2018 Fields medalists at August 1st in Rio De Janeiro Brasil will:
Simon Brendle ( Germany 1981  ) Differential Geometry
Blaine Lawson conjecture, Sphere, Ricci Flow
Winner of the 2017 prestigious Fermat Prize,Fernando Coda Marquez ( Brasil 1979  ) Differential Geometry
Willmore Conjecture Plenary speaker in ICM August 2014 Seoul, KoreaPeter Scholze ( Germany 1987  ) Algebraic Geometry,
Arithmetic Geometry
Perfectoid Space, Weight Monodromy Conjecture
(special case of Deligne Conjecture)
Plenary ICM 2018Geordie Williamson ( Australia 1981  ) Representations Theory
Conjecture of Soergel, Conjecture of LusztigKazhdan
Plenary Speaker IN ICM AUGUST 2018 Rio de Janeiro 
Scholze is a certainty. Williamson highly likely. Brendle 50% chance. Fernando Coda Marquez will not win for 3 reasons:
(1) Brendle is also a geometer and has done even more. SLim chance that two geometers are awarded in the same year.
(2) A Brazilian just won in 2014. Too soon for another Brazilian.
(3) The most important papers that Marquez published were all coauthored with another prominent mathematician, who is over 40 and is not eligible.
As to who else might win, don't overlook Wei Zhang (a prize to a Chinese is overdue; the ZhangYun paper is big breakthrough) and Ciprian Manolescu (singleauthored paper on the resolution of triangulation conjecture, based on a subbranch of math that he himself created).
The 2018 Fields medalists at August 1st in Rio De Janeiro Brasil will:
Simon Brendle ( Germany 1981  ) Differential Geometry
Blaine Lawson conjecture, Sphere, Ricci Flow
Winner of the 2017 prestigious Fermat Prize,
Fernando Coda Marquez ( Brasil 1979  ) Differential Geometry
Willmore Conjecture Plenary speaker in ICM August 2014 Seoul, Korea
Peter Scholze ( Germany 1987  ) Algebraic Geometry,
Arithmetic Geometry
Perfectoid Space, Weight Monodromy Conjecture
(special case of Deligne Conjecture)
Plenary ICM 2018
Geordie Williamson ( Australia 1981  ) Representations Theory
Conjecture of Soergel, Conjecture of LusztigKazhdan
Plenary Speaker IN ICM AUGUST 2018 Rio de Janeiro 
You’re an economist, not a mathematician. Economics is not mathematics regardless of what you aspies believe. Why should you care?
There is a substantial intersection between mathematicians and economists. Many economists have undergraduate majors in math. It's part of their roots.
Not to mention the ubiquitous math envy.

Anyone else thinking the system is unfair? You have to be under 40 in the year of the award, held every 4 years  so for some people their last chance to win it is when they are 36, while some others it's 39. Sure, this kind of big contributions are most likely done at an earlier age, but 3 years does sound like a big disadvantage.
10 reg monkeys have just started writing an RDD paper.
Scholze is a certainty. Williamson highly likely. Brendle 50% chance. Fernando Coda Marquez will not win for 3 reasons:
(1) Brendle is also a geometer and has done even more. SLim chance that two geometers are awarded in the same year.
(2) A Brazilian just won in 2014. Too soon for another Brazilian.
(3) The most important papers that Marquez published were all coauthored with another prominent mathematician, who is over 40 and is not eligible.
As to who else might win, don't overlook Wei Zhang (a prize to a Chinese is overdue; the ZhangYun paper is big breakthrough) and Ciprian Manolescu (singleauthored paper on the resolution of triangulation conjecture, based on a subbranch of math that he himself created).The 2018 Fields medalists at August 1st in Rio De Janeiro Brasil will:
Simon Brendle ( Germany 1981  ) Differential Geometry
Blaine Lawson conjecture, Sphere, Ricci Flow
Winner of the 2017 prestigious Fermat Prize,
Fernando Coda Marquez ( Brasil 1979  ) Differential Geometry
Willmore Conjecture Plenary speaker in ICM August 2014 Seoul, Korea
Peter Scholze ( Germany 1987  ) Algebraic Geometry,
Arithmetic Geometry
Perfectoid Space, Weight Monodromy Conjecture
(special case of Deligne Conjecture)
Plenary ICM 2018
Geordie Williamson ( Australia 1981  ) Representations Theory
Conjecture of Soergel, Conjecture of LusztigKazhdan
Plenary Speaker IN ICM AUGUST 2018 Rio de Janeiro
Point 2...I was not expecting that kind of reasons for a math prize....

Scholze is a certainty. The next in line is Geordie Williamson, followed by Simon Brendle. The 4th and final spot will be between Manolescu and Wei Zhang, with a greater chance going to Zhang.
Viazovska will not win for two reasons: (1) The sphere packing problem is relatively isolated. Solving it doesn't have a very broad impact on a major branch of math. (2) She is still young, will have 1 more shot in 2022. For Williamson, Brendle, Manolescu, and Zhang this would be their last chance before turning 40.
The 2018 Fields medalists at August 1st in Rio de Janeiro will be
1. Scholze
2. Brendle
3. Viazovska
4. Manolescu or Williamson or Zhang 
June Huh
June Huh will not win this time. He is still young (~ 31 or 32) and will have more chances in the future. Also, his most important paper on Hodge theory for combinatoric geometry is still under review. That being said, he is definitely a contender in 2022.

In the choice between Manolescu, Williamson and Zhang it will come down to the committees priorities among the following secondary criteria : subject and geographic distribution of medalists, single vs multiple authorship of main work, elegibility in future cycles. It will be a difficult decision. My hunch is that Zhang will get the medal in this group since he may have an edge in the primary criterion, namely originality.