And my kid started to talk at 2.5 years (mostly, only his mother and I understood him) and now at 4 years old, he is one of the most talkative and expressive kids in his class. He has better math skills than anyone in his class (and its a mixed 3 to 5 years class)
Up to 4-5 years old (and later of course but this time frame is where it is easier to do comparisons: kid speaks or doesn't speak vs kid knows how to multiply or doesn't) kids develop at different rates. Let it be speech or math or just general coordination (while my kid spoke gibberish at 2.5 years old, he was able to climb trees on his own and do an handstand at that age. He sucks at any kind of dramatisation or singing, but he knows a good amount of constellations and can identify them on the sky, and the composition (simplified version of course) of the earth, it's core, and how volcanoes work, etc).
Up to 4-5 years old (and later of course but this time frame is where it is easier to do comparisons: kid speaks or doesn't speak vs kid knows how to multiply or doesn't) kids develop at different rates. Let it be speech or math or just general coordination (while my kid spoke gibberish at 2.5 years old, he was able to climb trees on his own and do an handstand at that age. He sucks at any kind of dramatisation or singing, but he knows a good amount of constellations and can identify them on the sky, and the composition (simplified version of course) of the earth, it's core, and how volcanoes work, etc).