Funnily enough, this was nothing new back in the 60s, 70s or 80s down South. Be it Rekha, Shobhana or Sridevi, tall teens as the heroine in films was so common, no one raised an eyebrow. A teen or tween in fairly adult situations, the romances (albeit rather chase ones) with often much older co-stars... Er... different times.
As mentioned earlier, Sridevi was one of the few who worked with co-stars who were, 20+, 30+ and even 40+ years older than her. We've gone down that rabbit hole earlier, so let me not repeat myself. Not much has changed; watch this space, if Sara Ali Khan can work with Akshay Kumar, its just a matter of time when one of the Khans will work with someone 30+ years younger than them.