I have sailed in the solo cabins (actually called Studio Staterooms) twice and I would guess the average age is high 40s - both men & women. Definitely not all are there to "hook up," just the opposite. Most of them are very bright and well educated and just enjoy having some company on a cruise (who wouldn't prefer that?).
I personally would say more attractive women than men do it, because single men are not so likely to think of a cruise as a vacation (they would camp, hunt, fish, drive, etc). So, there are usually a good number of women but do not expect them to be "easy". In fact, although they are friendly I think a lot of them think of the cruise "hooking up" mentality as a bit cliche.
But after a few drinks, a moonlit night, a single cabin with "mood lighting" - who knows?