I am 46. I have a great sex drive but I can’t say there has been NO decline, like ctroadrunner.
I would say that until I was 40, I would never think about my erection. I could have sex anytime. I could even occasionally cum and not stop fucking until I came a second time. Probably around the time I was 40, there were times where I would feel that my dick during sex was not completely hard as a rock, especially after drinking alcohol. Still hard enough to do it, but not throbbing hard. I know this is normal for many guys, but was a new development for me. I was in my early 40’s and drunk, the first time and only time I failed to get hard for my wife. It effected my confidence, even though I know it could even happen to an 18 year old, if drunk enough.
Now I’m 46 and I have sex every day, and I beat off every day, and I’m horny as hell. As horny, or more horny, than I have ever been. I just enjoy it and my relationship with my wife is a big factor in my wanting to fuck all the time. I usually lose my interest in sex after drinking, but I can still have a few and fuck just fine. My erection is normally excellent, especially in the morning, but again, occasionally not 100% after drinking or tired. I would say my erection is better than many 20 year olds, but I notice a decline compared to when I was 20. I am in pretty good shape and exercise regularly, and eat low fat, and I know that is THE most important thing if you want to fight off ageing effects.