My daughter has gone at 8 months, 21 months, and soon 28 months. We're expecting our second who will be only weeks old on the trip.
Any age is a great age for Disney! I never personally understand why people won't take their kids because they won't remember it. I didn't beat my daughter just because she wouldn't remember it, right? My daughter STILL talks about our Disney trip, so even at this young age, she remembers.
At 8 months she was a blast because she wasn't scared of anything. She loved the characters the rides, the shows, just everything. We even took her on Pirates and into It's Tough to be a Bug. She slept through most of the shows, nursed everywhere, and just had a wonderful time. Feeding her solid food was a challenge since at home I make my own, and we had to bring the yucky jarred stuff. She didn't want to eat it. She was also too young for ice cream. The only thing she didn't like was the family raft ride at Typhoon Lagoon. It splashed her in the face and she cried.
At nearly 2 she was so much fun! She wasn't afraid of the characters, but was a little timid. It's Tough to be a Bug scared the bejeezus out of her, but she's a pretty easy going little thing and just snuggled into her daddy with her eyes closed and telling us she was scared. We won't be taking her to it this time. The character meals couldn't have been more fun! It's just such a delight to see her there. She really believes that it's all real, and to see the magic and wonder on her face is priceless.