At debut Tvxq, Bigbang and Shinee were all still teenagers. The oldest tvxq member turned 17 the same year they debuted. That’s the same age as Nct Dream and younger than Newjeans
I’d argue that the age span idols debut have gotten narrower. There aren’t as many extremely young idols debuting (tho they still exist) but there’s also less idols debuting in their late/mid twenties.