I can only say how it was for my older two.
dd1 was in her cot until she was over 3. Never tried to climb out (and she was tall - she could easily have got out from about 15 months). In fact, she was so settled in the cot (and we were so fearful of rocking the boat too much) that we bought another cot when dd2 was due, rather than turf dd1 out... then, when we did bite the bullet and put dd1 into a bed, it was all fine (we thought we would have major issues, as dd1 has severe ASD and so just the break in the routine terrified us) - dd1 took longer to get to sleep, but stayed in her room - either on her bed or curled up in the armchair flicking through books.
dd2 was in a cot until just past 2. by this point, the dds were sharing a room, and dd2 got frustrated that dd1 could get in and out freely but she couldn't. dd2 was a tiny little thing, and so had to work hard at climbing out
, and we were worried she would fall awkwardly, so we took the sides off. it was ok-ish. going to bed was more or less ok, but the mornings were hell as dd2 is an early riser, and so from 5am she was up and about and now able to roam...
ideally I'd like to keep ds in his cot until at least 2. his understanding now is quite good, but he is also right in the middle of pushing boundaries and finding it funny, so he would certainly be up and roaming if he thought he wasn't supposed to. hopefully by delaying a little we will end up where we did with the dds - where going to bed and getting some sleep wasn't a problem at all (but then given they never really tried to climb out, I'm not sure the comaprisons are useful as clearly ds is a different kettle of fish entirely!)