There is May December romance but I am looking for the equivalent that means Younger male - older female: is it January -June? (Also known as Noona romances) Older male - younger female: April- February? This should be a tip, I think Younger male- Older female relationships are classified as Spring romanced but I could be wrong
https://tvtropes.org/pmwiki/pmwiki.php/Main/MayDecemberRomance "Generally, the man is the "December" (elder) and the woman is the "May" (younger), though it can happen the other way around." ... AFAIK, you still just say may-december.