Leela
Yes, it's normal :) Especially with young gliders they tend to ride of their moms backs. My female was 4 months old or so when we got our 4 year male, she still gets on his back now n then until something else distracts her lol. She was probably just grooming him, but make sure you check for any injuries. Is your male glider neutered? if not I would get him neutered as soon as possible, the female is not physically or emotionally ready to breed until they are a year old. The male will not wait until she is ready.