1. What injection does a person at 16 years need to receive?

Question

2. What injection does a person at 16 need to receive?

3. What injection does a person at 16 years old need to receive?

4. What injection does a person aged 16 need to receive?

5. What injection does a person at age 16 need to receive?

(Which ones are grammatical? What other expr4essions can we use?)

Answer 1

I would use "vaccination" instead of "injection."

I would also rephrase: What vaccinations does a 16 year old need to receive?

All your sentences are grammatical, but #3 is awkward.

Answer 2

3 and 5

What injection(s) does a person need to receive by age 16?