18 years old still haven't finished is it me or him or both

Been having sex with same guy for 5 months now and he was my first but I still haven't finished is it normal or is it something we are doing. He's never went down on me but that's probably cause I never asked do u think that would help? And could how long it last be a cause to? How long do u usual last and is it penetration or stimulating Clitoris that finishes u?