As a nice guy in your twenties, you're basically hosed; the women you meet hold all the cards and they know they do. Most of them figure they don't have to date you because someone better/more exciting/hunkier is just around the corner. Let's face it, they are probably right, but it still sucks, as our American brethren say. As noted before, to add insult to injury, they often want to keep you as a friend and perhaps even cry on your shoulder about the obvious asswipes they are dating. Yes, just what you wanted!
However if you manage to evade capture until your thirties (and beyond!), you will begin to notice a very welcome, if belated, change. While you were the desperate one in your twenties, frantically searching for someone who would take you, as you get older you will find yourself having an increasing say in the destiny of any relationship you enter into. This is shown in the graph above, which shows the balance of power shifting from about the early thirties on.
Any woman of a similar vintage to yourself still single in her thirties simply can not afford to be as picky as she once was. Her chances of meeting anyone will have severely decreased as couples pair off, leaving her with less friends to socialise with and less suitable men to meet when she does go out. While the Internet has improved things in this regard, it won't stop the gradual panic (that she has missed her chance, that there are no good men left and that she will die a lonely spinster with just her cat(s) for company) from setting in. This is brilliant for you, the ageing and terminally nice guy. You can finally come into your own and experience what it feels like to call the shots in a relationship!
Granted, your choice of baggage-free contemporaries isn't as wide as it was either, but being a man, at least women five or ten years younger are now on the radar (without fear of being arrested!). This in turn forces women your own age to look increasingly upwards for possible partners, which makes you an even better catch for them! Talk about a confluence of positive factors! A nice guy at this stage is manna from heaven for a woman, who is looking for solid, settling down material, not the bad boy party animal she may have preferred in her younger days. Better late than never, I suppose!
However, you have to be careful, because when a woman of a certain vintage lands what she perceives as one of the last of the good guys, she can get clingy very easily, something you may not have much previous experience of. Also, no matter how tempting, you should not abuse this new found power by trying to exact revenge for all your past rejections. Nor should you settle because of social or family pressure. Just because you finally meet a woman who gives you the time of day, doesn't mean you have to settle down with her! No sooner have one set of problems disappeared than another appear in their place!