Difference between 几岁了 and 多大了?

Question

I googled a bit on it and found different explanations. Some says it just depends on the region and dialect. But my text book explains that as a rule of thumb 几岁了 should be used for kids before 10 years old, and for other cases 多大了 is Ok. Could you please provide some more explanation on it?

Answer 1

Your textbook is correct.

Answer 2

As a native speaker, I use both expressions to ask people who are significantly younger than me. And I will get asked these 2 questions by people who are significantly older than me.

Your textbook gives a reasonable explanation that 几岁了 is usually used to ask people who look like they are not yet at puberty age. And 多大了 can be used among all ages.

I answered this question according to my personal experience, and if anyone has different explanations, I am more than open to discuss!