I think you would do well as a wing or hooker. I play wing and it is my favorite because you get to run very fast and help your team score. You might also do good as a hooker in scrums and line outs. I hope I helped you out.
You could play number 9 or 10, where the physical size is less important than effective technique. 9 and 10 control the game and are arguably the most important positions in the field, but they take time to learn. I started as 9 when I was 11 yrs old then moved out eventually to fullback, but generally smaller nippy guys who like to talk (boss around the big forwards ) make good halfbacks. I would look at 9 or 10 to learn the basics of running the backline and when you grow in h coming years you could be a talented player with more size which will help you in the long run. The Welsh halfback is very big 1,9 metres and can use his size to complement his skillset as a .9... Give it a shot!
I would say wing I'm 15 5 foot 2 and 125 pounds and usually play wing I play in high school varcity team so girls age 14-19 but I also play inside or outside center and I may be small but I also played flanker so really u could play and back position or any lose forward postion
