While there is no legal age limit to fly in a balloon, most balloon ride companies will have thier own age policies.

We've found that very young children (under 5 or 6 years old) are often frightened by the noise of the burner. Another rather interesting thing we've noted is that young teens are sometimes bored with a balloon flight -- go figure! We guess that since the flight doesn't have the excitement and g-forces of a roller coaster, some youthful passengers lose interest pretty quickly.

Since each company will have their own policy regarding minimum passenger age limits, you need to discuss this directly with them.