hmm this is really a tricky request since most dramas are more with a coldish/reserved FL and a younger sweet ML.
My Love from the stars - technically he is actually older than her, since he is an alien, but he is in the body of a young guy who is her junior. It is very sweet and very funny Secret Boutique - the main focus is revenge and not romance but there is a coldish female lead and her younger assistent that fills your wish.
