A lot of it comes down to a young person having quicker reactions and being able to intuit game mechanics faster, and also there’s is more access to the underlying mechanics of videogames than compared to previous decades. Plenty of How-To’s, guides and Let’s Plays give people an easier understanding on how to excel.
Is it possible for an older person to rise to the top? I think do so but too many factors are stacked against them. I myself play Overwatch regularly, i’m in my late 30’s and it’s hard to keep up with the need to react quickly and precisely but i do my best and i still have fun. Though i know i’ll never be able to compete at a high level and i’m ok with that 
