GAW: There is no halacha in Torah Sh’baal Peh which states that the act of attending College is ‘assur-prohibited’. If your Rebbi/Teacher/Parent encourages you to not attend college until after your marriage and strive to live a higher standard of Torah life and you choose to follow, then that is very commendable of you and you will earn more reward in shamayim for this; but please don’t state that attending college is ‘assur’.
On a different note, if one attends college and sets himself behavioral “gedarim”-red lines which he commits himself to never cross, then he will be able to preserve his yiddishkeit there and not fall prey to all the harmful influences he may encounter there.