Friend of mine who has had a kid explained this to me for anyone else who's kidless like myself.

I guess the development rate of kids is sorta all over the place and various facets of development are benchmarked at certain months not years.

So parents speaking to other parents this probably makes total sense and they know developmentally where the kid is based on months.

For us non-parents, well, thank God our phones got calculators eh?

Knowing 2 years is 24 months is like.. Rocket science?

To be fair, a 6 month old is different from a 12 month old.

more annoying when it's already a multiple of 12

One mother once told me the kid is 73 months old or something like that... the kid seemed like he was 5, 6 or so...