How to train toddler to sleep through at night ? Sttn 😴

I have a routine that I been following through when my kid was 2 months old. he naps regularly, and bedtime is always 8.30pm. in the day he will have outdoor activities, at least twice a day. he eats well too. # Sttn 8.30 pm lights off. although at times he takes around 1.5 hour to go to sleep. he really sttn when he turned 18 months old,.prior to that he will still wake up 2-3times a night and then gradually decrease to once a night. some toddlers takes earlier or longer though. when toddler is ready, he will be sleeping through the night.