I’m tall when I’m young, and I’m short when I’m old. What am I?

satin. 

"very shiny satin may look great in the fabric store or in the sewing room, but once onstage it can look fake and cheap as it reflects the light from the fixtures."

these are the choices for the answer?

this exemplifies - rondo form

your word would be isle.

isle is an island or peninsula especially a small one.

if you add the letter "a" you get aisle, which is a passage between 2 rows of something like chairs, shelves, or something else.