It is really hard to tell from pics with a hammie but I think Pebbles looks most like a Pearl Winter White. It is impossible to age a hamster from a picture but pet shop hamsters are rarely as old as 8 months so I wold say a bit less than that. It does look like a mature adult though.
The pic of underneath is blurry but I think I can see a yellowish scent gland on the tummy. This is typical of a male hamster. Males can get quite stained with the yellowish scent secretions which does not happen with a female.
Sometimes it is hard to see the testicles in young WW or indeed adults if they are cold.
Females have nipple lines and males do not. Can you see any nipples?
Anyway you have a beautiful hamster