You can take it either way you want, really. It doesn't matter that much. It's pretty hard to believe somebody could live 29 years and never see a dead leaf. Never see a dead ant. I mean, sure, the servants could catch the leaves. We can buy that one. But could the servants have caught every single dead ant and worm and whatever else might have crawled around the ground that little Siddhartha would have seen? So, yeah it's hard to take that story for perfectly true word for word. The actual essence of it, is what this person mentions: yeah, there is a lot of people today, who are 29 years old who have had nothing but tons of happiness in life, they are the rich kid, and they were growing up getting everything they want and then all of a sudden, Daddy just died. They're not so happy after all. So there are people whom we can identify with as the main part of the story.
The Buddha as a rich, young prince would have not grown up normally. His father gave him everything. Maybe he saw some of the leaves turning brown whatever and the ants dying, but he didn't care because he was always being distracted by the fun things in life. And maybe at age 29, he did go out in the carriage and maybe he did actually see these things one day after another, that part may actually be true.