Is this random? Or based on something? If so, what?
Age based is one part of it, the separation line is 18, I think. Also, users who have been recently online tend to come up more, and maybe users whose things you've commented on or answered.
If you mean similar age groups, then I guess it's not working. The people suggested to me are usually about a quarter of a century younger than me ;)
Well, it's more along the lines of 18 and over, and under 18.
Age group and online status.