what is the difference between this sentences?

Hello everyone! Can someone explain what is the difference between this sentences?

I could have moved out when I was 18

I could move out when i was 18

In fact i don’t see any difference at all!

If you are looking back to a past opportunity then use the first one.

The second one seems less likely, but I think it could be used in a future-in-the-past sense (i.e., within a past-tense narrative, looking forward to the time when you can move out).

Remember that “I” should always be capitalised, and that sentences end with a full stop (or question mark or exclamation mark).