Retinol? (21F)

I saw a video made BY A dermatologist. He said that if you REALLY wanna age well, it would be good to start in your 20s. He recommended CeraVe Retinol (the blue one)

I'm very insecure because I think I look a bit older than 21 and my skin looks really bad in general.

I'm gonna buy the retinol. I just wanted to know: Will I get all old-looking if I stop using it? Will there be any negative side effects in general?