My 3 and half year old son seems to fall a lot. Should I have his eyes checked or could this be just age related?

Falls. Children fare on top of the list for all age related falls. It's no wonder to see their shins and often arms full of bruises. If you are concerned about your son's vision, you may watch him closer whether his falls occurs outside of "normal" circumstances, for example, like he'd bump into walls, doors etc.
Yes. If you have any concern your child is not seeing properly, have him evaluated by a pediatric ophthalmologist.