years old
 

The question of a paper is

-How old was John when he was attacked?
-How many years old was John when he was attacked?

If the answer is 'three', one mark; if 'three years old', no marks. Do you agree with the marking scheme? I think 'three years old' is wordier, but not wrong and should deserve marks. Somehow the setter of the paper explicitly says the inclusion of 'years old' makes an invalid answer.

Re: years old
 

The second version of the question is unnatural - we always say How old and not How many years old. As always, I've checked with a concordancer and there are no examples at all of How many years old in the corpora.

Either answer is acceptable however, and should be marked right if it's a comprehension question. In spoken English, it would be more likely for Three years old to be prefaced by he was however. You could say :

A : How old was John... ?
B : Three or He was three.

or
A: How old was John...
B: He was three years old or (possibly but less likely) Three years old

I checked a concordancer of spoken English and in 15/16 examples of British English the expression XX years old was preceded by the verb BE. In American English BE was used in 6/9 examples. So if conversational skills are being tested (and in that case why is it a written test) either is possible but He was 3 years old is more natural.

Re: years old
 

Excellent answer. Thank you.