You might want to talk to a fertility doc to confirm it, but since you're only 21 and haven't been on HRT for very long, I'd say that (provided you were fertile prior to starting HRT), your chances are excellent. However, you'd need to come off hormones altogether for an extended period of time - at least 6 months and maybe as much as a year. This is because it takes about 4 months for sperm cells to mature, and on top of that you need to allow time for your testicles to recover from the effects of the hormones.