I did it as soon they started to attempt to climb

My daughter went from cot to her own bed at around three years of age.

I think it depends on the child. I’m going to wait & see when I feel like its safer for my son (when it appears he might be able to climb out of his cot I’ll transition him to a toddler bed). My nephew had just started climbing & his mother thought he was asleep in bed & heard him crying & found his in the middle of the floor at 21 months old& he had fallen out of the cot & broken his wrist. I guess its hard to know.

when they start trying to climb out of the cot and begin to walk

Usually the transition from cot to bed happens when bub becomes too big for a cot. Mine were around 2