To obtain a Private Pilot Certificate in the USA you must be 16 years old. Yes, although balloonists seldom do because of decreased visibility and the requirement for instruments and lights. Most balloons are certified for day flying only. A gas balloon is completely enclosed and is filled with helium or hydrogen. A hot air balloon gets its lift from heating the air within it.
Balloons generally launch at sunrise, or in the last couple hours before sunset.
The primary reason for this is that winds through the middle part of the day are often unsuitable for safe flying. Additionally, the mid-day sun's ultraviolet rays can prematurely degrade the chemical coating which is applied to the envelope during manufacture. While it is possible to fly in winds of 10 knots or more, it's not particularly safe to do so. Generally, it is preferred to fly when surface winds are 10 knots or less. Winds of 5-8 mph are ideal.