Yes balancing on two moving wheels is an important skill
The same way as you would ride in any other place.
bicycle
No. Most any passenger car will suffice. Some people drive a motorcycle or even ride a bicycle to get there.
any age
No, when riding a bicycle on a one-way street with two or more traffic lanes, you should ride in the rightmost lane that is going in the direction you are traveling.
you can ride a dirt bike at any age
The word BIKE in this question is a little vague. Obviously a bicycle can be rode on any road without a permit.
Any old how. Some will ride the Team Bus. Many will fly. No one will go by bicycle.
If there is no bike lane, then the appropriate place to ride is on the roadway. As a slower vehicle you must abide by the rules of the roadway and allow any traffic you are holding up to pass.
Well, you can either get a motorized bicycle, electric, or gas. Or you can get a fairing, like the windscreen and cowls on motorcycles. Or you can get a bicycle at allows you to get into a low and aerodynamic tuck to reduce wind resistance. The extreme applications being faired recumbents and velomobiles.
depends on where you live, where you ride, and what the law says about an unicycle. If you're on private property you can ride anything and any way. Where I'm at unis are legally seen as toys, and not as bicycles, which means that bicycle helmet laws don't apply.
You should be 16 to ride in streets or pretty much any age to ride on your own property.