All 3 of my boys were out of diapers by 2 1/2. Nathan my youngest was my only cloth diapered child and he took the longest. We did the naked method which is something you may want to discuss w/ his mother. My oldest slept dry by 18 months and was completely done at 25months. Pooping was an issue w/ 2 of my boys. I ( at the advice of my ped) gave them lots of prune juice 2 - 4 oz a day. There was no holding that. After 2 or 3 sucessful runs to the potty they were "unafraid" ( for lack of a better word). In my family it would be quite odd to be 3 and still in diapers. I have 5 nephews and all were out of diapers well before 3.
To OP maybe the mom needs some cooperations and suggestions. I have seen children be diaper free in daycare and still use diapers at home.