Preemie

My son was born 4/3/21….11 weeks before his due date and the drs keep saying he will be 3 months behind cuz technically he was supposed to be still in the womb but since he’s out of the womb wouldn’t that make him 3 months a head technically his CJA is 2 weeks so technically he’s only supposed to be 2 weeks old but he’s 3 months does that mean next month he will start laughing or will I have to wait until he is 6-8 months cuz he’s 3 months behind? I’m gonna ask his dr Monday but I just would like opinions from mothers in general