Why are my balls always hard. my balls are never sagging! is that normal?

Likely normal: That is likely normal. However, it only one testicle feels hard, the issue should be evaluated by a doctor.

Size of scrotum: Testicles tend to hang low/sag with a pendulous scrotum, will also make testes feel softer. Non-pendulous or smaller more svelte scrotum will prevent testes from sagging ; also make them feel relatively harder. There is a wide normal range with regards to scrotal size. Intrestingly, have had couple of young men present with concern about pendulous scrotums ; ?Possibility of reduction scrotoplasty.