Hello,
Thought I might give my opinion on this. Well, I'm 23, and in a relationship with man who is much older than me, and I'm not talking just 10 or 15 years here. It all depends on your mindset, maturity level, and if you have anything in common (God only knows that you'll only last if there's at least a few things in common, other than sex). Another important factor, at least I truly believe, is the way he treats you. To me age is just a number. I'll tell you that I'd rather be with an older man, than with some 20 year old who wants to treat me like garbage, and not be serious about things in life. I've been through enough.
So, that's my opinion. I am treated by my older man with the utmost respect and caring that one could ask for. All the stares and gossip doesn't put a damper on our relationship. So to me, there is no "acceptable" age limit if you are an adult.
With all I've been though, I have a more mature mind then some my age, so I guess it can't work for everyone.