I weaned DC1 and DC2 fully off the breast by 13 months, DC1 was mix fed anyway. Have since met a few other mums who let their babies decide when to stop and it sounded much much nicer. DC1 wasn't a prob as he was used to other milk, took cup quite early etc. etc. DC2 had to be weaned on to a bottle and is still on it 6 months later - I think needs / needed the comfort to be honest and I feel a bit mean for rushing it. I started off gently but eventually said the milk was all gone.
So if you let him or her self-wean would they just drop it slowly for themselves? Did you gently encourage them? The 'natural term' babies I know stopped by 18 months ish anyway. I am not meaning to start a debate about weaning but its something I'd like to consider for next time.