Because you are not on the dining plan you will be able to order whatever you like. You can choose to share with another person, order an appetizer instead of an entree or order from the children's menu. Once in a great while someone will post that a server, usually at a non-Disney owned restaurant, will adhere to the 9 and under ages printed on the kids' menu, but very rarely.
You cannot share and everyone will be charged according to their age, regardless of how little they eat, at buffets (e.g. Crystal Palace, Tusker House), All You Care to Eat family style meals (e.g. 'Ohana, Garden Grill), dinner shows (Hoop De Doo, Spirit of Aloha Luau, Mickey's Backyard Barbecue), fixed price meals (e.g. CRT, Akershus), dining packages (e.g. ROL, Fantasmic), dessert parties (e.g. MK, Star Wars), special events (e.g. Dine with an Imagineer or Animal Specialist, Food & Wine events) and anyone who partakes of the Family Platter at Whispering Canyon Cafe.