Jaz was 13 months. Only fell out once, I had the fold out couch there JIC.
Bri was about 14 months. We just started by taking the side off the cot. She stayed in it like that til she was 2.5.
Jesse's cot converts to a toddler bed, but I just don't see him as ready yet. Now he's mostly sleeping through I might do it soon, but not til I know he won't wander the house in the middle of the night, lol. I also have rails that will go on the sides, once the cot sides come off.