I flew for the first time with my baby girl when she was 5 months old.
She did great on the plane.
Make sure you keep that diaper bag stocked with exactly what you need!
I forgot to put an extra set of clothes and wouldn't you know... the one time I forgot, she had a little blowout and OMG. I had to open our luggage and pull out clothes. It was a little hectic.
If you nurse her, (I did) make sure and bring along something to cover yourself with in case you have to breast feed in case your plane is late. It happened to us.
I had a sling too and that was GODSEND!
I nursed her as the plane took off to avoid her ears popping.
And I gave her a little dose of tylenol in case her little ears hurt due to the pressure in the plain.