I've heard that there are quite a few mid-single group activities (campout, Powell trips, cruises). If you feel like you've got a high level of ambition/achievement, then it may be good to seek activities where similar people would be.

Church-sponsored singles activities have a really low barrier to entry, so you get all sorts of people. Classier/more expensive/more commitment-heavy activities will naturally weed out a lot of people.

It's the blind leading the blind here, good luck.