If you're single, date a middle-aged person
(Inspired by something I just e-mailed to a family member, who is single.)
Here's my theory: if you're on the dating market, try to date a middle-aged person.
Middle-aged folks are more stable and predictable: as a buyer, you know what you're getting.
People change a lot from their teens to their 20s to their 30s. But by the time you're around 40, you know who you are, and what you like (and don't like). Your personality, your temperament, your lifestyle, your interests: your twenty-year forecast is more predictable by your 40yo status than your 20yo status.
As a 45 year old, you know what your political views are. You know whether you're a drinker or not. Whether you're a smoker or not. Whether you exercise or not. Whether you're good with money or not.
If you're going to end up overweight, you're probably showing it about now. If you're still pretty slim at 45, you're probably going to still be slim at 65.
It's unlikely that your 45 year old partner is going to unexpectedly take up a new hobby: it's not a midlife crisis -- it's finally getting around to doing something that she/he has always wanted to do (buy a sports car; buy a boat; learn the electric guitar).
At least, that's what I reckon. But I'll let you know once my cohort hits 65, to tell you whether I was correct. :)