Personally, i think that Chinese girls mature quicker than European girls, as in Europe it is common to still be single and having fun into well into your 30's, i'm 36 and still go clubbing, go to gigs and music festivals etc, but as someone already has mentioned and also experience from a girl i was writing to, most Chinese girls over the age of 25 who are not married have a name in Chinese, apparently it translates into 'left girl' so if you are over 25, or divorced or have a child already, a lot of Chinese men would not consider them for a partner, as i often saw in China, guys who looked in their 30's/40's with Chinese wives who were in their early 20's. It may be a reason why a lot of these girls over the age of 25 are happy to leave their country in the name of love as they are of an age or in a position where a man in China would not consider them for a partner. Also, i do not think a large age gap is that bad, tho i would not really consider a girl more than ten years younger than me. You have to remember that if she is young and you are old, and it is her coming to you and not you moving to China (i think if you go to her country a large age gap is more likely to work, as she would not change her thoughts and values) when she arrives into your country she will become westernised to a certain extent, and if she is young she will naturally want to go out and see and experience new things. I keep hearing these stories of these young Asian girls (under 29) marrying these guy's in their 50's/60's, she wants to go out to see all these new things, but he is more interested in who is cooking his dinner and wants to relax indoors and watch tv, it's not surprising it does not work out really. Well they're my thoughts maybe you do not agree with this but i have seen a lot of failed 'mail order bride' marriages over here, mostly when it is a large age gap.
Cheers,
Andy