And that's a problem how? Like FO says, It's all through the mind. Figure out your psychological trigger & make that your goal in a session. Or not if you want to be Mr. Endurance. I often have the same "problem" & can wear myself out & give the poor SP muscle cramps if I can't hit my trigger. Today was one of those days so when it became clear at the 45 minute mark, I gave the lady a break & finished out the hour with some cuddling & a massage. And that was fun too.
A different SP I've see a few times seems to accidentally find my trigger way too soon in the session before the fun really starts & I'm done. So I don't tell the ladies what it is to avoid becoming another two-pump chump. I find it much more fun to participate in this hobby with a bit of mystery.
I know who I'm going to see.

I know that I am going to have sex.

But I don't know how it will end.

And that adds to the fun. & fun is what we do this for.