What is the youngest someone can use a gun?

At shoot straight almost any age but they have to be supervised at all times. Also use common sense dont give a high caliber to a kid that would not be able to handle it. Like for example you wouldn't give a 5 year old 70 pounds kid a 50BMG for him or her to shoot would you? If you think that's ok then you should look for another range to shoot at . BTW 50bmg is not allowed to be shot at shoot straight.

Any age as long as there are with someone 21 years old or older.

I would call ask for cassie

I'm not sure, but i wouldn't think younger than 9-10. .22 caliber is a great round to learn how to shoot with. I'd give them a call, they'd be more than happy to answer your questions.