Re: is this normal at my age?
You're growing fine for your age. Your penis grows until your 20s so you have plenty of time left for it to grows.
Condoms will probably fit but they really aren't designed for pre-developed teens anyway but they do sell smaller sizes worst come to worst. But you're 15 you shouldn't be worrying about sex.
Girth is the circumference of your penis - basically the length around.To measure you can wrap a string around the circumference of your penis, then take the length around and compare it to a ruler