I'll be forty in a few months. My libido has definitely increased as I've gotten older. I'm not sure how much of that is a result of no longer having small children and leaving a repressive religion and how much is a result of getting older.
I do find that in the last 11 months that I've been dating my boyfriend, my libido has shot up drastically. Before I started dating him I had one tertiary partner that I had sex with a few times a year and my husband, who I had sex with about twice a week with at that point. My boyfriend has a much quicker recharge rate than my husband, coupled with a higher libido in general. For the first couple of months that we dated we'd have marathon sex sessions every time we got together. It definitely slowed down some after we'd been dating a few months, but we still have more sex than I do with my husband. And I've found that having more sex has had the effect of making me think about and want sex more often. So I think right now it's a combination of getting older and an effect of poly.
Isn't this phenomenon part of the reason for cougars? Older women searching out younger men who can keep up with their desire for sex? Pairing the peak of the male sex drive with the peak of the female?