I'm past 65 and usually go for 2 shots in an hour to 90 minute session. I don't think there is any magic in it. I'm pretty horned up when I meet my date and try to work the first shot in the first 15-20 minutes. Then work on her for 20-30 minutes, then we work on me either just her or together for shot 2. Or as I do with several of my regular MP's they give me a great 30min massage in the middle part of the visit. This leaves me about a 5 minute clean up shower and voila, I'm rested, calm, mellowed out and can handle any stress coming my way or have a great sleep, whatever seems appropriate. For me its my level of being really horned up and I strive to stay healthy.
Note there is a difference between multi-orgasm and multiple shots too. Where multi is several in a row and multiple is more than one spaced out. I have experienced a few multi's with one particular woman I was in a relationship with some time ago. Only time. Fuck if I know what the deal was. I mean she had these stunning 36DD's and could work her pelvis like anything but I would pop, then keep on and have another O, then another all within a couple minutes either vaginal or in her mouth. Geesus it was Awesome! The multiple thing, pretty sure any reasonably healthy guy is going to be able to do it.
To the OP go into your next session letting her know you are looking for 2x, one in the first 15 min the second in the last 15 min. I'll bet you leave twice as happy !!