My kid was also borne in Dec. She is now in a relatively good kindergarten that has primary and secondary school. No need to worry to get into P1.
Same as some other parents, my opinion is let the kid try first before making a decision.
However, parents need to do more work to train up your kid in order to keep your small kid up to standard so that she/he can be comparable with others including those "big" kids.
I recalled when my kid went to interview 2 years ago, she also had many unsuccessful cases. But one successful case was enough. I took her to interview class, different kind of English classes (drama, english playgroup at different centres etc., few times a week); putonghua classes etc... This also enhanced her skill in meeting stranger.
Some parents may say this will bring pressure to the kid and parents needs to put much effort and time. But you can recognise the reward - your kid getting into a good school! Up to now, I think this is luck, but because the effort we put on the kid.