About 2y 4m - everyone on here acts like that is late but it was still earlier than most of her peers we knew at the time to be honest.
The signs of readiness were showing an interest in the potty we'd had knocking around for ages (she would line up her toy ducks and make them all wee on it, then started sitting on it herself). She'd tell us when she'd done a poo. And once we were at playgroup and she grabbed my hand to pull me towards the toilets saying 'wee wee mummy' (and then proceeded to do one on the loo) so we took the nappies off from that day really.
I think having the potty around, talking about what it was for, reading a picture book called 'No more nappies' and the fact she always accompanied me to the loo so knew what went on all helped get her ready.
We tried to stay home for a couple of days at first, though I think we did actually go to a class on the second day as she'd pretty much nailed it for wees from that point on. Nappy free, reminding her regularly. Got a travel potty for taking out and about, it still lives in the car now if we're ever caught short!
She was dry in the day pretty much instantly, and at first the poos seemed to be going well but then we had a bit of a setback with that and she started witholding which led to some leaking/ accidents and the whole thing got a bit traumatic for a couple of weeks. Watching the 'poo goes to pooland' story/ app really helped, but in the end I cracked and say to her 'if you do a poo poo on the potty you can have a chocolate coin' and that pretty much solved it instantly! I felt really bad as she'd not really been allowed chocolate up till that point, but it was definitely a very effective tool. Also led to delightful situations like when DH went to the loo in a cafe, she screeched at him as he was coming back 'you done a poo poo daddy? You need a chocolate coin?'
We had a couple of regressions - once when we went on holiday we seemed to get quite a lot of accidents which stopped as soon as we got home, again when she started school nursery just the first week, and again starting Reception just the first week.
What we seem to have missed the boat on is nighttime dryness - 4.5 and not had a dry night yet. I'm really not sure what to do for the best there, had lots of conflicting advice. I genuinely believed it would just follow automatically somehow, but obviously not.