Also, don't worry about the cipher yet. Two Hearts is quite a rabbit holey puzzle, start off by treating parts of it as a normal riddle and seeing what happens from then on.
I think you're thinking the right way, ish; but you're not following the plain text instructions that are given. there's not much else there, so it stands to reason that they're important. :)
I might have underestimated the difficulty of the first paragraph. I showed it to a friend who got the answer straight away, so I assumed it'd be a nice simple first step to ease people into the puzzle. Oh well.
(Feel free to ignore everything I've said. I'm still confident the answer will be obvious when you work out the meaning of the lines. Or the meanings of the word.)
Googling the music bit will explain the 'underage'
I'm not sure, this is my first riddle and I wanted to do something a bit different, which is why there are a lot of steps after the riddle. Was the riddle part bad?
I have keys, but I have no locks.
Some consider me majestic.
Other find me annoying.
I can do back, but not forward.
I am happy.
I am sad.
I can hold you in suspense.
What am I?