A is angry at B for being kind to somebody and says that. They are both young adults.
It should mean "No matter the age, you are good at being a good boy!", but I don't understand the logic of いくつ. I need a more literal translation, word by word.
I've found いくつになったら, it's similar, but it's a question, mine is not.
Can you say どこになっても, 誰になっても, 何になっても and so on too, when you're not asking a question? If so, can you make some examples with other pronouns too, please?