Just used 4 years old photos for my 16 years old son - no problem (and in that age it’s a big difference) and I’m also using my old photos where I had 20 Kilo more - never had any question
Regarding travel bubble you have to wait for final a announcement - e g if it is with China would it be only for Chinese people or also for other nationalities who are coming in from China - not sure If that is clear and even with travel bubble they seem to limit the total number of people coming in
i just did 90 days report for my son (BKK) app was not working but Website worked well (did it late in evening and was approved very early next day) - so I recommend to use website instead of app