Well I'm 19 and my boyfriend is 17. We kinda found out we liked each other on my 19th birthday so I haven't really thought about the oldest I'd date since I'm with him. I suppose if I wasn't with him then the oldest I'd date at my age would be a 24-25 year old or something. That said, I decided when I was 18 that I wouldn't date anyone younger than 17 then ended up seeing a 16 year old for a bit although it was innocent. I then decided when I was 19 the youngest I'd date would be 18 and here I am with a 17 year old boyfriend. Plus, when I was 18 I had a crush on a 33 year old celebrity so it could go either way really.
I say don't worry too much about age difference as long as you like each other but obviously don't do anything inappropriate if they are under 18.
I don't think it matters personally. Everyone has different preferences. I mean I've seen girls 25o n this site talking about being into 50 year old men and if thats what they like then I don't see a problem with it. As long as the two can find a connection and bond then I would feel happy for them despite the age gaps.