I think its up to individual.
I'm in my mid 30s, and I do it at least once daily.
Sometimes when really horny, I'm able to cum 3 times within 2 hours. Need to continue maintaining stamina to appease my fbs.
The only time I couldn't get hard was due to excessive wanking over a period of 3-4 days (cumming more than 7 times per day). Took me almost 2 weeks to recover from that ordeal. I guess age really does affect stamina.
