Balding is not related to testosterone, but rather Dihydrogentestosterone (commonly referred to as DHT). Although high testosterone levels often mean high DHT levels as well, it is possible to have high DHT whilst still having low testosterone levels.

The amount of androgen receptors in your scalp is also relevant, some people are just unlucky and have lots of androgen receptors in that area and start balding at a young age despite average DHT levels