The fact that you think that it's normal for a 30-year-old to say that he loves and misses his 18-year-old 'best…
It's actually quite the opposite, people used to get mature and responsible quite earlier back in the days. Now you may look mature but even an 18 years old can't take responsibility like old days.
The article
https://kisskh.at/article/kim-soo-hyun-s-agency-denies-the-actor-was-in-a-relationship-with-kim-sae-ron-when-she-was-a-minor
The source
https://n.news.naver.com/article/001/0015265717?sid=103