14-16 hours direct Houston to Doha and return at 6 weeks, and 6 months with one child and at 1 yr with another child. We have three childern seprated by 2yrs. We have done 4 other round trip shorter flights, 4-7 hour direct, with our youngest which is now 1 yr. All the flights we have taken with our youngest and middle child were without issue.

As others stated I don't think an under 6 month old will limit how far you can travel. At that age they will adjust quick to time change or won't be affected by it at all. I think the most difficult time to travel with a child is around 1yr when they want to explore and are crawling/walking.

Limiting factor for us if it is one parent flying alone with all three and the timing of layovers. Trying to carry a baby (plus carry-ons maybe car seat) and a 2yr which are asleep through an airport is a nightmare, especisally if the 4yr will not wake up to walk with you. You always can't expect the stroller to be avilable during a layover. So we don't take flights with layovers during the kids prime night time sleep.