The nasty thing about "male" or "female" libido is that individuals never have a "high" libido.  Nor do they have "low" one.  In fact individual people don't even have average libidos.  Not even the average ones!

Instead all individuals ever have are... libidos.

Ok, actually, they have libidos and partners.

Partners who may (in fact probably) don't have libidos identical to theirs.

See, the problem we have is looking at individuals as if we were in the aggregate.  Which of course is fine in the aggregate!  Except, of course, again, we're individuals rather than aggregates.

This lack of absolute high or low libido isn't particularly a problem.  I mean, sure, if one does have a partner, or maybe a prospective one, there can be negotiation and frustration or satisfaction or whatever.  But left to our own devices we're pretty much horny now or we're not.  Unless maybe we're Samuel Pepys we don't really chart it.

This, as I say, isn't particularly a problem.  Except, of course, in the context of partnership.  But for the most part we have a lot of social scripting and narratives for coping.

Until we reach somewhere a little north of middle age, anyway.

After middle age a certain problem can arise.

It arises out of the confirmation-bias-leaning phenomenon of individuals when left to their own devices only saying "gee, I'm horny" when they are.  But never really "wow, I'm sure not thinking about having sex right now."

The problem being that up until slightly north of middle age, men are defined -- by themselves, by society, and often by their partners, as the baseline-normal of libido. 

Again, he grows up never really having to think about being horny when he's not because, in the normal order of things he's ususally horny before his female partner so a) she pretty much never has to wait for him and b) he pretty much never thinks "I'd better get up to speed here, she's putting the moves on me."  (You probably remember hearng narratives about men thinking about baseball statistics and great aunts to slow themselves down.  Remember all those narratives of men urgently skimming fantasies in order to get themselves caught up with their partners?  No, I didn't think so.  It might happen but there's not a lot of social scripting for it.)

Anyway.

Somewhere between, say, ages 55 and 65... maybe a decade earlier, maybe a decade later... men stop being horny as frequently as they were in, say, their teens or even their 30s.

Very often, at some point, their partner's libidos -- the ones which might have been "lower" for the first few decades of their relationship -- can become higher.

Sometimes considerably higher.

Which, if you only notice when you're horny, and especially when you've grown up thinking sex only happens when you're horny...

Friction can arise for which there's not a lot of social scripting for coping.

If you're conscious about such things... about recognizing it when it happens, and acknowledging it... then you're probably going to be fine in your relationships.  Maybe not great, maybe still a little frustrated or a little harried in ways you didn't grow up expecting to be.  But still, if the possibility is on your horizon you'll still probably be fine.

If not?

Look out.  Not all unexpected surprises are pleasant ones.