If he truly is taken, I agree with this. However, I've seen a lot of older guys in "relationships" with much younger women and found out that they were in an open relationship, or were really only dating without the expectation of a relationship...etc. If he really is in a serious relationship, you have to be prepared to accept rejection gracefully though. Also, there is the possibility that he may tell his girlfriend. For me personally, if I was dating someone and some other girl approached my boyfriend in such a way, I wouldn't be angry at her for it. It happens all the time, and he should be prepared to deal with it appropriately, if he really is a respectable guy.