Balding patterns very confused

[Basketballhead]

I've never understood the Norwood scale. My hairline is perfect and my temples are where they should be for a man in his early 20's. I have mild/moderate thinning in the entire horseshoe shape on the top of my head. Because I'm thinning at age 21 am I gaurenteed to be a norwood 5 or 6 in a few years or do I have a chance. I am currently on finasteride and using nizoral and seriously considering a hair transplant in the near future if my regimen stabilizes my hairloss.

Any advice???