When can I renew my son's passport

[motherforceawakens]

It runs out next June. I'm renewing DS2's at the moment. Can I renew DS1's even though he has over 6 months left on it? We have a few trips planned next year and it would save me time if I could get them both sorted out now.
Thanks

Yes renew it now, passport office will add any unused months from old passport on to your DS’s new one.

Anytime you want.

I believe they only add unused months up to 6 months. However if you have trips planned in the first half of the year there isn’t much you can do but renew now.

It's 9 months added on (assuming UK passport) so you won't lose out of you renew it now.