20-Year Prospect
In the world of professional gaming, there's no twenty-year prospect. Esports are volatile, and sponsors and tournaments only reward the best. The problem for you is, "the best" changes constantly, otherwise things would get boring pretty fast.
So if you can't hang on for the better part of one Earth lap 'round the sun, what are your chances doing this for two decades straight? We'd say somewhere between zero and negative three.
And if that wasn't bad enough, there's that whole problem of the games themselves losing favor or being replaced by new fads that you're just not as practiced at. While you're cashing in on League of Legends successes by running the Fields of Justice fifty times a day, some other young upstart is putting the same amount of time into Fligglety Bits, some bizarre up-and-coming game you've never even heard of.
Two years later, when Fligglety Bits gets big and League is dead, that kid is now 100,000 hours of skill ahead of you. And no, you're not going to catch up.
Fortunately, with only about forty people in the U.S. able to play games for a living in the United States, chances are you'll never have to deal with this issue, because you'll probably have burned out and taken another job long before twenty years have had the chance to pass (source).
Those who remain successful in this field must build themselves as a personality that people will want to see. If you've got enough charisma, you just might be able to become a commentator someday and remain in the spotlight. Otherwise, have a backup career planned out.