His thing is shooters. Pro gamers like that have a shelf life. It's not like other sports where you can compensate with slowed reflexes by reading body language to predict where things will go to a degree. Say some boxers can go on at a high level to 40 or older but as a pro gamer in that genre you need the reflexes you start to lose when you're in your mid 30s.
There's some truth to this, as our reflexes declining with age isn't in question, but its very game dependent. Rapha and Cooler are still at the top of the Quake scene and both are in their mid 30s. I dont know much about COD but with most shooters you need a baseline level of precision, after which factors like strategy/teamwork/comms/leadership become the deciding factors. Most pro gamers retire in their mid/late 20s (or earlier) but there are generally other factors around that, most notably how top heavy the market is and how priorities tend to shift for men coming into that stage of their lives.
A bigger question is whether his chosen game will still be around, you see many pros in their mid/late 30s still playing the game they came up with, but transitioning from one game to another is very hard. Older games like Quake, Warcraft 3, Brood War and DotA all have big players who are considerably older, cause they just kept going.