I took my daughter to Florida when she was 7 months old and it was fine. On the way out we had a sky cot that sat on the table by the bulk head. On the flight back we just had an empty seat next to us. She slept going both ways. Can take a little longer getting through security with a buggy and extra baby bits but the actual flight was fine.
I've also taken her to Majorca at 1 1/2 and Egypt at 2 and it was fine on both these occasions although on the Egypt flight she slapped the bald guy in front on the head much to my amusement