Student or Learner
Does this make sense?
I think it should be "college days" or "in college".
I have lived in Seoul since college.
The original is OK. The only ambiguity is that it's not clear whether the speaker went to college in Seoul and has lived there since starting college, or if he/she moved to Seoul immediately after finishing college.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.