It's common sense that the good ones are always taken. Let's face it, when you desire a woman because she is attractive and likable of course tons of other men will feel the same way about her and try to lock her down. Most women are locked down by the time they are 25, anything past this is very unusual and there is generally a reason for it.
Seriously, it is in a man's best interest to try to find an attractive and good girl when she is in her late teens or early-mid twenties and try to get into a relationship with her. Past a certain point you are going to find that the women that are single are so for a reason. Getting into your late twenties through early 30s you are going to find that the women available to you already have a kid or two, which really is a major issue.
I'm 29, I workout regularly and take care of myself so I'm very fit and will age well. I went to a speed dating event in April and to say the least I felt very out of place there but it was also an eye opener. Literally all that is available to me are women well below my league, not just physically but in regards to where they are at in life. If I could give my younger self advice it would be to become far more proactive with trying to meet women, because the pickings become increasingly slimmer the older you get. I'll come across women that are around my age and I don't even recognize them as potential dating prospects, but when a significant portion of our country is overweight or obese it is understandable.