Leg sometimes goes dead what does this mean am only young ?

Nerve Compression: For most, a limb "falling asleep" just means you need to change positions so that the nerve is not compressed and then it will be fine. There are other reasons for abnormal sensations or weakness, though - spinal/bone issues, muscle or nerve diseases or infections, etc. If your leg "going dead" is frequent, getting worse, or really starting to seem abnormal, talk with your doctor.

Nerve or blood flow : Moist likely nerve compression either at the back or in the leg. Could get an EMG to check it. Could see a neurosurgeon to evaluate if you need imaging MRI of the back. Should also check the pulse in the legs to make sure there is no problem with the blood flow.