20yr old... can i back squat with heavy weights even if my legs are slightly bowed?

Go ahead: It's a trade-off between doing what you want to do and the possibility of back and joint damage down the road. I agree you're not at much increased risk compared to your peers. Do talk with your personal physician first; there's little science in predicting who will and will not be able to undertake a super-aggressive training regimen successfully.

I believe so: You should not have problem with that.Good luck.