他多大了用英语怎么说

"How old is he?"

This question can be translated into English as "How old is he?" It is a simple and direct question that asks for the age of a specific person. The answer to this question would depend on who is being asked about. If you know the person's name and are asking about their age, then you can simply ask "How old is he/she?" or "What is his/her age?". If you don't know the person's name, then you may need to ask around or look up their information online.