I brought my girl at 18m (she’s petite and able to fit into bassinet but only willing to stay inside for awhile). Most of the time she will sit on me facing outwards (they will provide another seat belt for baby to attach to your seat belt for take off and landing).
took our 16m old, already too long for the bassinet, but he slept through both flights, going there and back.
you can still call the airline directly to see if they can arrange a seat for you.