It's probably fairly new, that being a subjective term. IOW not antique, I'd say seventies looking. The term for the part of furniture at the head of the bed frame is headboard. ;-) Not trying to correct you so much as if you ask someone else, so they know what you are referring to. I dunno what it is, but sure looks from the picture like is sits atop something else, like you said.

It's a headboard from the late 1960s or early 1970s at the very earliest. Its kind of country-hippy-Holly Hobbie fushion.

It appears to be a headboard from a waterbed set. Post 1970 for sure; most likely from late 80s early 90s.

It would have bolted on to the waterbed frame from underneath, probably using L brackets.

My old boyfriend's waterbed headboard!

BTW, those things were usually really SOLID pine, so if you need some sturdy shelving, take it apart.