I wouldnt worry i would go with what he wants ...if he feels secure and still fits the cot let him be .... he will protest the cot when he doesnt want it any more...

My first son who is 12 now went into his big bed at 3 and he was in a protable cot with a foam mattress ..but he loved it and i loved it as he couldnt get out lol.... NO devemental detriment with my boy !!

And my ds who is 2 1/5 loves his small cot.....and i will just go with him ....

Its like bottles the kids wean them selfs.....