As one example:
Do blitz players get faster or slower as they age?
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in karpov's case im pretty sure he only plays rapid and blitz tournaments nowadays.
he made some very wise investments in a oil company and is now a billionaire.
Greenhouse gasses - Checkmate, Planet Earth
how many hours do you spend on this site?
You can't make wise investments. The financial world is all a game of poker.
I can tell you this blitz player has gotten slower with age , and I suspect every blitz player slows with age , and not only in chess . 
In athletics there's definitely a cutoff point where one assumes the athletes are past their peak and declining. Is there an assumption about age and speed in the chess community?
What ages are typical peaks? Have there been notable exceptions?
And, is the decline in speed/strength in blitz reflected equally in standard chess Or is it more typical that the curves are phase shifted such that the blitz speed tends to slow while standard chess games improve?
Who are some of the older chess champions or titled players who have been able to hold their title in active competition as opposed to holding their rank by retiring from competition?
Is there an age where it is generally expect that one generally cannot match their former greatness, similar to athletics?
I understand there must be exceptions.