Not from HRT directly, no, but here's a stretchmark story for ya~
Back when I played a wildly popular MMORPG (no, not WoW) I got them. I was playing this virtual time vampire for like 15 hours a day; no job, no social life. I'd eat, poop, shower, sleep and play the rest of the time. It was soooo ridiculous but I couldn't see at the time how harmful it was. It was a game that even gained a nickname amongst players called Evercrack (yeah, that one!).
So my mom bought me this foam grey cushion because she knew how much I just sat on my ass doing this and my chair back then wasn't soft. Well after a few weeks I got these really horrible purple stretchmarks on my inner thighs and it took awhile for me to figure it out. The material was this like no-slip grippy foam wedge that was literally pulling my skin away from my groin the way I sat on it. Soon as I threw the cushion away, they went from purple to pinkish but it took years and years for them to turn white. They're still there: a permanent reminder of the trials and tribulations of being a hardcore raid-pro in an MMORPG, LoL! So my stretchmarks weren't age or weight related.
Point is: Maybe yours are genetic. Maybe your growth was phenomenal and nothing could be done. But maybe it's due to some outside influence... too tight of a bra? I don't know; just offering a different viewpoint.