People’s real nature is usually revealing itself pretty soon in relationships. Few months the most. Unless someone is complete scammer and con-artist, then it maybe could go on longer, otherwise it’s pretty obvious. The trick is to pay attention.

I don’t think age matters. Unless you do prefer older men, I don’t think specific age will matter at all

Certainly you shouldn’t give up at 28. In fact this is just a start for looking for serious relationships. Many people aren’t even considering it at younger age.