My DD is only 2 1/2 and is 18kg.

But she is just big all over. We had nude kids here earlier in the week and we were laughing that although she does wobble a bit more than most (no rolls but more covering) she is literally 4 inches broader across the shoulder and a half a head taller than any of her peers.

I'm not worried about her weight at all - she eats healthy and exercises every moment of the day (I can't find the off switch!)

If you aren't worried then don't worry what the "rules" say.