Upvote:2
My kids, back when they were underage, used to travel all over the place. Airlines worry about young children (their upper limit for "young" varied from about 5 to 10), but for teens, no problem at all. Domestically, they do not even check ID.
I definitely got the feeling that if a toddler in diapers could somehow get his passport up on the counter, Immigration would wave him through.
We were told to give the child a permission letter, signed by both parents and notarized, and originally we did, but after several years without anyone even asking for it, we gave that up.
Upvote:10
Can younger travelers have their own visas, yes.
Can they enter the country without a parent or legal guardian, depends on that country's rules.
Will the airline take accept them as passengers without a parent or legal guardian (UM or otherwise), depends on the airline's rules.
Getting the visa is the easy part, but likely needs a parent's signature, not something they can do totally on their own.