Camoflage clothing acts as a visual illusion to animals by "breaking" the image of your body up with foilage. When blending in to leaves, wearing camo, you become nearly impossible for animals to see.
It depends on the store. Most likely 15 or 16, but I know stores like Zumiez, etc. require you to be at least 18 years of age. It depends what state and country you live in too. If you are under 16...