Barrgghh
Wrong in DotA and AOE 2.
That being said there is some advantage to being young, but experience is quite impactful in less twitchy games.
I think the biggest problem in rocket league is the amount of practice needed to maintain a pro level of play. Once these kids grow up and need to start handling adult life, rocket league doesnt really fit in.
I think if it were possible or reasonable to pursue professional rocket league as a career, we would see older players.