There’s no certain age when he will stop waking up at night for milk. My son is 2 years and 2 months old, and he still wakes up for milk. Not everyday though, but occasionally, maybe around once or twice a week.
If u want to wean off, u can try giving him water instead of milk. But do it gradually. Like if he usually drinks 150ml of milk, u try giving him 100ml milk, and 50ml water. I heard that works, but I never try on mine.