This can happen at any age. I was dating someone who is only a year younger than I am but has vastly more relationship experience including marriage and kids. And yes, when someone has this kind of history, whoever they're dating later on tends to get the short end of the stick sometimes because they gave most of their effort to partners in previous relationships. They don't often realize they are doing this but it happens. Sometimes, it's expected that you simply take whatever is left, or whatever they have the capacity to give, and not expect as much as previous partners did. Of course, this is unfair to new partners since they're not the cause of any hurt or pain the person experienced in previous relationships.