I've got stretch mark both on my hips and a lot on my inner thighs, both of them are from my sudden growing (yes sideways 🙁 ) during puberty. It sucks, but they should lighten slowly, although they won't all dissapear. I used to have tons of them on my chest from the same thing (I grew up fast suddenly) and they've become almost invisible. What's helped me is seeing that other guys have them too! Even on hips and chest. Or sometimes I consider them like battlewounds but that'sprobably just a strange me-ism.