With Maddy she was about 15mths & I set up the bed which was in her room, she climbed up on it & wanted to sleep there so i left the cot next to it for a few dyas & then took the cot down as she just wanted to be in a big girls bed!

With Indah we bought bunks so her & Maddy could share, the top for Mad & bottom for Indah (bottom is a double bed too so plenty of room!) But she will play on it & sleep in it if DH or I lay there with her, she wont with Maddy (which is what I had originally thought the 2 girls would sleep together for a whyile making it fun!)
Indah will fall asleep Dh & I will get out & 10-15mins later she is pitter pattering down the hall way saying HI! We try to put her back but she kicks & screams & yells that she wnats to go in her cot, we put her in there & she immediately lays down & goes to sleep!
So they are complete opposites & it's an issue at our place at the moment as we chose not to keep a bassinette/cradle as we figured Indah would love sleeping with Maddy in a big bed! But nope!

So I think iut's really when your kid is ready... However I am thinking if he can easily climb in & out now, I'd start trying day sleeps, after all he can't fall out of it!???

I hope you have better luck than we are!!!!