Wow!! Thank you everybody so much for the positive feedback, congratulates, and personal insight! Just be reading some of your replies, I now understand that there really isn't a right or wrong age range. We're both huge Disney fans (as are all of you awesome people!) and we're just so thrilled about sharing this experience with our child!
I was originally adamantly against taking kids before they were 4 or 5 since they would not remember anything about the trip.
Of course, I've now taken the following trips in the last 3 years:
1. Spur of the moment trip to
Disneyland while in LA -- DD1 was 26 months old and and DD2 was still in the oven.
2. WDW trip #1 - DD1 was 34 months old and DD2 was 6 months
3. WDW trip #2 - DD1 was almost 4 years old and DD2 was 18 months
4. WDW trip #3 - DD1 was 4.5 years and DD2 was 26 months
5. WDW trip #4 - (leaving this weekend) -- just a trip with my DD1 and myself (the dad) to celebrate her 5th birthday (6 weeks early).
The first trip was really nice. DD1 rode all the kiddie rides and met some characters, and napped in the stroller as needed, while we just bounced around from ride to ride with zero upfront planning (you can do this in DL). We got there at park opening and left right as park was closing.
Second trip was good too. But it was a completely different beast staying at WDW and dealing with a stroller and the buses. With that said, the 6 month old just slept in the stroller for the most part, so she was super easy to take care of. We pretty much took turns riding stuff with DD1 using the rider switch feature.
Third trip -- my 18 month old was a terror. She wanted to walk all the time and she melted down probably 5-10 times a day (even with leaving the parks everyday to nap). One of us had to leave every single table service dinner before we were finished b/c she was just such a mess. My oldest never had any of these issues at any age...so it is entirely child dependent.
fourth trip -- my youngest got a bit better, but she is still stubborn as hell and will start crying the second she feels slighted. She just might be the death of me...hopefully this is just a phase. hahaha
All of that to say -- taking a 6 month is actually pretty easy. However, the 6 month old won't enjoy it at all. At that point, you're just going for yourselves and to get some fun photos. Since you only have one child, I would probably wait until he's around 2 or 2.5 years old. That way, he'll be old enough to recognize the characters at least. It's so much fun to watch their faces light up when they see a character they recognize. Fair warning, a lot of kids get frightened of the characters (especially the masked ones) until they're about 2.5 or so. It took mine quite a bit of time to warm up to them. She loved watching them from a distance...but got shy as soon as they approached her.
In any case, there is no right or wrong answer. It's all about what you are wanting to accomplish that will more or less determine "the best" time to take them. Just recognize that anything before 3 years old is mostly for your enjoyment in seeing their excitement. Good news though is that their tickets are free if they are under 3 years old.