I've generally stayed till mine were asleep until at least age 2 - I know some don't like doung that, but it worked so well for us, and they went to sleep quickly.
My eldest: once she was 2.5 I'd say goodnight and leave her awake. Could usually hear her singing/chatting to her teddies for a bit. Used to come out at least twice, probably lasted about six months. Never made a big deal out of it, just gave her what she wanted and returned her to bed. I figured if she felt she could come out if she needed to, she wouldnt need to. It was a bit annoying if I'm honest. Sticker chart on her bed when she was 3 - she got a sticker if she didn't come out. Definitely still occasionally popped up. Really only got reliably sorted once she could read herself independly.
Next two kids took a dummy at bedtime till they were 4. They shared a room and did chat many nights but usually stayed in their room after 2.5ish. Bloody brilliant at bedtime now at age 5 and I think it's because they have each other for company.
Youngest doesn't go to sleep indeoendently yet. I should probably bite the bullet, but she goes to sleep within ten minutes if I s5ay and she's DEFINITELY the type to keep popping up for a drink/wee/another story if I tried it, so right now I'm opting for an easier life.
I don't think you can really force it. If they are comfortable and happy then they will learn to do it. Some are more anxious or more active and will need help for longer. When someone else's children are ready won't necessarily tell you when yours will be. For my boys, room sharing has been really positive for bedtime, but I have a friend who finds it a nightmare for hers - although they are 8 & 6 she has to stay until they are both asleep or they fight!
They all do it eventually. Support them in feeling comfortable and confident at bedtimr and the rest will follow in time.