Is it normal for a 16 yr old girl to have spider veins? I have noticable spider veins on my left side thigh. I'm starting to notice that some are starting to appear on my other leg. I don't know why I'm getting them at my age. I'm average weight and eat

Puberty. Heredity and the hormones of puberty are the most likely causes. If you are taking a birth control pill, that can play a role as well. It probably doesn't have much to do with standing, inactivity, what shoes you wear, and your weight. Crossing your legs when you sit down doesn't play a role at all.
Hereditary factors. Spider veins are not the norm for a 16 year old girl. Most likely there is a hereditary component. Hormonal changes may also play a role. For now the best treatment would be staying physically fit and physically active. If the look of the veins bother you, then sclerotherapy could be considered. Most likely you will develop more vein with time.
Genetics. Genetics determine just about everything. A this point in science we can't run away from it. Discuss this issue with your parents first and then your doctor. Good luck from nyc.
Yes, . Yes, you are very young to have spider veins. Spider veins typically present in people between ages 18-35, peaking after the age of 50. Risk factors that precipitate spider veins include being a woman, genetics and heredity, also if you take birth control pills, lead an inactive lifestyle, are on your feet alot, or wear high heels often you increase your risk. Things you can do to reduce your risk factors are staying active, keep your legs elevated when at rest, wear compression stockings, mainatin a healthy weight and move your legs whenever possible.