Thru my 20s, 30s and 40s, it was usually 15 to 20 minutes once or twice a night. In my 50s, I have started on Friday evening and have had sex through late Sunday night, with alternating fucking and oral sex, one following the other, with just short pauses for food and a few cat naps. The lady had 12 orgasms in a row at one interval while I had one cum session. It takes a special woman. We'd go to work for 8 hours, have dinner and then fuck all night again with oral in between the fucking sessions. This lasted for months on at a time before we took several days off the rigorous schedule. We couldn't get enough of each other.