Backward-looking (13)
'backward-looking' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for retro that I've seen before include "Backward looking" , "Imitating a style from the recent past" , "Old-fashioned style" , "Fashion of yesteryear" , "bit of nostalgia" .)
(Other definitions for retrospective that I've seen before include "Looking backwards" , "Looking back" .)