Characters in my story range from 5 - 80 - I'm an ageless god.
Secondary and side characters can be any age just fine for me, lead characters though are a different story, I'm not going to write a lead character who is too much older then me, basically because I have not lived that age yet to know the little nuisances that would go into being that age that I usually like to include in characters to make them feel more real, something that's going to be a lot more important to factor in when you're dealing with character leads. When I get to that age, then you'll of course see more older characters as lead characters pop up.
This of course does not count those 'ageless' or 'Actually I'm 1237 years old' characters.