I flew with my first when he was 10 weeks and he was absolutely fine. I'm flying on Saturday with my 3rd who will also be 10 weeks.
We started flying when mine were 12 weeks and it’s much easier when they are tiny! We’ve done some mega 15hr flights and it’s always been absolutly fine - we have never had any issues. As they get older it harder as they don’t want to sit for that long. But plenty of snacks and puzzle games gets you through. You get free travel up to 2 but we actually booked his own seat for him when he was about 14months as it was just easier to have more space.
Fly whenever you want, I flew at 4 months and I have a friend that flew at 3 weeks 🤷🏻♀️ next time mine flys he will be 11 months x
As soon as you want, in fact it’s easiest when they are teeny. We started flying when our daughter was 9 weeks and used the under 2 discount as much as possible! Never had a bad flight, she’s 2.5 now and has done over 20 flights.