When talking about age we don't use any verbs, for example:
What about when you need to deny someone's age? Do we use 不是 or 没有?
Yes, we use
没有, for different meaning.
我不是二十岁。 I'm not twenty years old. (Probably 10, or 30, ...) 我没有二十岁。 I'm less than twenty years old.
PS: You could use
是 such as
我是二十岁 to emphasize the fact (that you're twenty). And when asked with the specified age, we usually answer it with using
When asked about the age generally, we usually answer it without using