Boxer underwear is the best! The briefs are very restrained, which will hinder the development of the penis during development and easily form penis bending; There is not enough space in the penis and scrotum, which may lead to some inflammation or sperm production problems in the long run. Wearing boxer shorts during the development period has little pressure on the penis, so it is recommended to wear boxer shorts designed with U-shaped bag. If possible, wear boxer shorts made of modal or bamboo fiber fabric, which has good air permeability, good elasticity, comfortable feel and drooping feeling, while cotton underwear is airtight, which is easy to heat up the testicles and hinder development. I think if you create a good space environment for the penis before it develops, I think you will develop well. After all, you are only 12 years old.
I hope my answer can help you.