The old days can always be missed, but the homesickness is merely just a symptom of the first tentative steps into something new. You'll be asking yourself what you were missing in a months or so time.
I'm 31 now and someone recently asked me that if I could go back in time where would I go to?
I said somewhere about 5 to 2 years ago IF I MUST!! Thing is that each step like school, uni, first job is simply just that........a step to the next big thing. Your life isn't laid before you, you make the choices every morning that lead you forward, just remember to take the path that looks the most fun then you'll have lots to bore your grankids with when you're old! :D