My LO was born at 28 wks. He didn't get his first tooth until he was almost 7 mo. but he started drooling constantly at about 5 mo. I had to change his shirt every 2 hrs or so. I tried keeping a bib on him but that just made him rash under his chin.
Its never too early...some babies are born with teeth. My son was also born at 30 weeks, he started teething around 5 months (3 months corrected age) but got his first 2 teeth at 9.5 months (7.5 months corrected age)