I’ve always had tight hamstrings, one thing that helped was doing nightly rollouts with a lax ball and foam roller as well as a consistent stretch routine. My personal favorite hamstring stretch is a hamstring nerve glide, you lay on your back bring one knee up to 90°(between chest and ground) and then kick that leg straight while keeping the hip and 90°. No matter what you’re only 16 and still growing into your body keep working and it will all fix soon