Just a general comment on toilet training - it seems to be left till later these days, possibly because of convenience of disposable (?) nappies. My own 5 children were all trained between 2 and 2 1/2 - one of them trained herself before 2, just sat on potty and started using it, copying older brother. Others took less than a week to get the hang of it, but we did look for readyness before starting.
First grandchild was trained by 2, in fact she started doing poos in potty before 1 - seemed to prefer it! Parents and (and me, when minding her) would just watch for signs and put her on potty.
There is a significant environmental impact to later toilet training - large number of extra non-recyclable nappies produced, though most people wouldn't consider this aspect. Obviously children mature at different rates, so one can't generalise but I still think lots of children could be trained at a younger age than the current trend.