Singular they - How old are/is they? [duplicate]

Question

I was wondering, because I couldn’t find that information anywhere, which version would be correct.

Let’s suppose somebody is telling me about :-) their :-) friend. I don’t know anything about the gender of that friend yet and I want to know how old... and here’s the question:

1. (...) how old they are.
2. (...) how old they is.

It’s about one specific friend that I don’t know the gender of.

Of course I could ask: „How old is your friend?” Or „How old is he or she?” but I’d like to use Singular they if possible.

So, should I ask: "How old is they?" or "How old are they?"? Or maybe Singular they doesn’t work here?

Answer 1

According to Longman Dictionary of Contemporary English:

‘They’ can be used when talking about someone who may be male or female, to avoid saying ‘he or she’:

If anyone has any information related to the crime, will they please contact the police.

Every child, whoever they are, deserves to have a mum and a dad.

People do this in order to avoid suggesting that the person can only be male, or to avoid using longer expressions such as 'he or she', 'him or her'. This use is acceptable and very common in spoken English, and is becoming more acceptable in writing as well. However, some people consider this use to be incorrect. You can sometimes avoid the problem by making the subject plural.

Considering the words in bold, one should use "singular they" with plural verbs.