Welcome to the forum. Without knowing when your turtle hatched, you really can't accurately know the age. You might ask the place where Ralfie was purchased about how old their turtles are when they get them (hopefully someone knowlegeble will have an idea).
Yes, it would be good to get rid of those pebbles. There are a lot of them, and at the very least, they're going to trap debris and make cleaning harder. If your turtle gets bored or curious, he may try to eat them, and if he does, there's the chance he could get impacted.
How big is the tank? Does he have a good basking area? Does he have both a UVB light and a heat light? Does he have a submersible water heater to keep the water at a constant temp?
What are you feeding him, how much and how often?
He looks cute.

"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-