An interesting twist on a popular topic (age differentials).
Personally, I use age in searches for a whole bunch of different reasons (trying to find a guy that I've seen in real life, trying to see how many people my age are on a site, looking for people with my birthday, etc.). So the real test for me is on dating sites that ask for the age range of my potential match. For these, I never use a range of some + or - centered around my own. That assumes that we all mature as people in a linear relationship to our physical age, which is so not the case.
So I use a very wide absolute range, which is 25 to 50. I pick 25 for the low end cause I think that age has just as good a shot at mental maturity as 55 does (with many exceptions, of course -- there are some amazingly smart and mature 22 year-olds on this very site). I pick 50 for the high end because, in my own very personal experience that doesn't apply to anyone else, I find that I have very little in common with folks that age and older, even tho they are only a few years older than me. And they most often aren't interested in me either, once they figure out who I am. I almost always get slammed for this, but I have stopped apologizing for "not acting my age" and this post is part of my "coming out" process