Hello, im 22 yrs old. start noticing blue veins on the back of my legs, especially on the other side of knees. could this be varicose?

Probably: Varicose veins are more likely in women, and can run in families. What you are describing does sound like it could be varicose veins.

Could be: As dr. Lerner said, you certainly could be describing varicose veins. If these veins are still flat and not bulging, my hunch is that you are seeing prominent reticular veins. These could be normal (meaning they have normal flow through them) and just quite visible or they could be starting to become varicose because the blood in them is refluxing (going backwards). If so, see a vein doc.

Reticular Veins.: There are essentially 3 types of veins-spider veins, varicose veins and blue or reticular veins. These blue veins are also called feeding veins because they can be leading into spider veins. Fair skinned people tend to have more easily seen blue veins. There is no proof that these blue veins will progress to varicose veins. If you have a lot of these veins you may want to have a venous sono.