My son just lost his first tooth (age 7). Is it normal that it bled for a few minutes?

Definitely! The blood vessels that supplied the tooth had to separate from the tooth; that's where the bleeding came from. If you wrap an ice cube in a wet washcloth, it'll help stop the bleeding and help any pain. Good luck with the 'tooth fairy' tonight!
Absolutely. The blood vessels in the jaw connect to the vessels in the nerve of each tooth. Sometimes there is a little bleeding when a baby tooth is lost. Usually stops quickly. If not, have child bite down on a 2x2 gauze sponge for about 15 minutes.