wow thats pretty awesome for a FIRST composition!
you dont have to follow rules. but since your waltz is super tonal and sorta Chopin-ish, i think you should have more dominant chords in your piece. i didnt even see one dominant chord in your piece. >.< (yes, im a very dominant dominated person.)
bar 7 or 17, for example, would be a really nice place to have a dominant chord doing into your tonic chord in the next bar.
i noticed you do have a middle section. but i dont think its enough to satisfy a climax-hungry listener like me. hehe.....
you should build up your theme more. cus its sorta repetitive right now.
you can also switch things up a bit, so that its more than just "right-hand-single-note-melody + left-hand-normal-accompaniment".
i also feel that you can make your ending stronger. you can either use a stronger cadence or.....i dont know, do something to make it BOOM.
but come to think of it.....lol, nothing i said is really NECESSARY, its just my opinion. :P
its nice to hear music from someone my own age. :D
:mellow: