you're right
Age and chess

There is: the older you get (starting from a certain point), the slower your brain works. That said, people still can perform amazing at a very old age; just look at Karpov, who is, what, 66, and still plays top quality chess (2.6k+ ELO).

Studies show your thinking and recall rate diminish with age, but doing things like chess, crossword puzzles, reading complex sheet music, etc. can keep the mind sharp to very old age - but it's still not what it was in your 30's.
If you are not a master, then there are things you can learn to improve your chess ability that more than offsets slightly slower thinking and recall.
Is there an age after which the performance of chess players decreases? (As in sport for example)