I am 56 and I had sex with my friend’s daughter yesterday. She is 18yrs old. We didn’t use a condom during intercourse. I ejaculated a lot into her vagina but during that she pained a lot. What would be the reason behind the pain? Does age factor make difference for that? Is it sexually safe to keep such relationship with her? Please advice.

Morally this is wrong. Girl much younger than you and that too friend’s daughter! Her pain is normal phenomenon and it has nothing to do with your age. There is a risk of pregnancy if you are not taking due precautions.