Why would my friend's health insurance premium lower than mine?

[Kross]

I read of a story of two friends that went to get a health insurance. And after everything, the premium for one person was lower than the other.
What are the likely reasons that one person would pay a lower premium than the other for health insurance.

 

[Nomad]

There are a lot of factors that determine your health insurance premiums, for instance, age, health, etc.