Giving head

Me and my boyfriend have been dating for almost 3 months. He is really experienced and not at all a virgin, but he was my first kiss and the first person i have given head to. sometimes he talks about how it takes him over 12 minutes to finish when i give him head but was able to finish a lot faster with other girls who have given him head. i know he doesn’t mean it to be offensive or mean but i kind of take it to heart. is there any way i can be better at it or any tricks i should know? it’s not hard it’s just i have a generally small mouth and i get tired easily.