Many people today, think that they are on a unique personal journey of self discovery. We are all on a journey of discovery. That is the very nature of being human. We can do it alone or in company. Its not unique, its normal.
If you get married young and you have not grown much as a person yet, you might yearn for the opportunities that you percieve others to have, regrets in this circumstance are what coveting thy neighbours wife is all about, yearning for something that is not yours. The thing is, personal growth is achieved by growing as a person and through overcoming the problems and puzzles in life.
I was married young and think it has been a great adventure. When you are too young, you don't know much, but you get a long time to learn with your partner and things you do together increase your chance of success.
I have had the opportunity to watch others get married along the way and it seem to get difficult for some. They become desperate to have children and then everything changes in life for them, faster than at any time previous. This seems to be a group prone to many regrets.
Too old and you know exactly what you want so it is difficult to find a partner but when you do the relationship has a good chance of success. Plus if you are lucky it might actually be till death us do part.
To sum it up regrets are a personal issue and a person likely to regret something will always find something to regret.