Ignome well at your age it is normal to have a girlfriend near the same age as you are. But I don't see the problem if a 18/19year old has a 15/16 year old girlfriend.
Offtopic you will notice that all 15/16 year old girls act the same way at least if you know them a bit. They always try to play with you and try out how far they have you under control hehe
. Just my experience in the past.
Final statement keep away your hands from kids up to 13 years. You could damage her for lifetime physical and mental.