Kind of a broad question but in case the powers that be decide to keep it ...
"Vintage" means nothing more than denoting an identifiable period of time. Whatever you can do to invoke your chosen time period is fair game. It's a gestalt impression, not one particular piece of the puzzle.
Analyze the techniques, motifs, palettes, typography, and subjects used at that time (by choice or limitation) to find its distinguishing features. In your example, the combination of jewel tone blue with bright red or the avocado green are period colors. The typography, on the other hand, lacks the hand-brushed technique to back up some of the implied vintage. Sometimes compromise is necessary to hit the deadline ;)