Do you think he's younger than the Gang of Five (I doubt it, but do you?)? Do you think he's the same age as them? Do you think he's a teenager? (Seems likely). Or do you think he's an adult? (Possible.)
I must say, maybe they should make a LBT movie where they bring back Guido and find out his past. I think, if done right, it would be a hit!
Guido is about as popular as Chomper, and, like Chomper, fans will be ticked if he never shows up again in a future movie.
His voice, which is one of the things I love most about him, makes him sound like he's not younger than the Gang of Five.
However, his voice almost makes him seem a bit older than them, though I cannot say by how much.
Hyp's voice, though older than the kids, still sounds like a teenager, yet Guido's could pass for an adult's.
We don't know how big a Microraptor gui grows in LBT as we've only seen one so far: Guido.
Thus, we cannot guess his age by his size either.
Of course, Guido isn't the only one that we cannot guess the age of. Mo, whom I also love his voice and appearance, is also a mystery, though I think he might be an adult as I never see his parents.
Guido's forgetfulness also helps none in guessing how old he might be. If he could recall more things, we might know more.
Of course, we really don't know the ages of anyone in LBT, but we can't even guess relative to others in the case of LBT, other than Guido is obviously older than Chomper, Tricia, Dana, and Dinah.
Still, what is your guess on his age?