Is it healthy for me to be 30yrs old and only weigh 108? I can't gain weight. Been wearing same clothes since jr. High school.

Could be. Depends on your height. Enter your height and weight into a bmi calculator (http://nhlbisupport.Com/bmi/bmicalc.Htm). If your bmi falls between 18.5 and 24.9, you're in the normal range. If bmi is less than 18.5 and you have trouble gaining weight, talk to your doctor.