I don't keep having the same dreams, but in all the dreams I have I keep seeing people I know, but not as I know them, I see them as younger and they're not always people who I knew when they were younger or whatever.

I can't work out what that could possibly mean, or why it keeps happening?

It could mean that something that has happened to you in waking life is reminding you of something from your past.

The dreams could be telling you that you should look back at what you have learned from past experiences in your life in order to deal with a situation you are in now.

If the people in the dreams remind you of any particular qualities, the dream could be telling you to examine those qualities (or the lack of them) in yourself.