年龄(nián líng) - age (of a person) in Mandarin

年龄 (nián líng) is age as a measurable quantity: the thing a form asks for, the thing a study controls for, the number of years between two people.

In real conversation you almost never use it. Asking an adult their age is 你多大？ and asking a small child is 你几岁？. 您的年龄是多少？ belongs on a hospital intake sheet or in a job interview, and used at a dinner table it sounds like an official filling in a box.

That is the trap. English "age" covers both registers with one word, so learners reach for 年龄 in casual speech and land somewhere between formal and odd. Keep 年龄 for writing and forms, and use 多大 when you are simply chatting.