I don't think so. It depends on whether the younger lead is much more popular or not (like idols and traffic actors) and how much is the age-gap. I remember when Cha Eun Woo starring a drama together with Kim Nam Joo, a lot of people hating it but it turns out to be a melodrama with FL treating him as a son. But it's completely okay for Son Suk Ku and some people even hating the ending because he ends up with the younger counterpart on Heavenly ever After. Not watching both.
For younger woman, I think Shen Yue-Jerry Yan pairing? Also not watching it.
As for me, I kinda like age-gap. For example; Story of Minglan (C-historical drama), Majo no Jouken (J-taboo romance drama), and Goblin (K-fantasy drama).