I read somewhere...(maybe it was here as Gogar mentioned) that the "rule" is:
1/2 your age and add 7.
So a guy who is 38 can go as low as 25.
Sound good? I mentioned this to a friend of mine recently and he was very pleased that 25 year olds were still in his range.
Now...what if you were 90? then 52 year olds are fair game and within the rules.
Seriously though...I think it depends on your mentality and how your jive together...get along etc. If you are comfortable then go with it and have fun. We only live once, for a short time....and never let anyone else dictate what you should or should not do with your life, as long as what you are doing is legal and moral.