Citizenship for 14 year child

[tier2013]

I would like to apply for citizenship for my son who has been on ILR so far and thats ending in 2024. Is it a straightforward application? His mother and I both have PR and his younger sister is a citizen on account of being born here. He, however, was born in India but has been residing continuously in the UK since 2007 (four months after his birth).

Please could someone tell me what forms and documents are required? Also, his Indian passport expired in the midst of the pandemic. Someone told me that the citizenship application for UK can be done with an expired Indian passport. Is this true?

Thanks for any replies

[CR001]

He can apply when either parent also applies.

[tier2013]

Does this mean he CANNOT apply unless either one or both parents apply?
Edit: I would like to make an application for him alone, at this stage.