I'm guessing the ages kinda do make sense if all three different personalities manifested at different times. Monster Mugo was probably the first and original personality making him the "oldest", Jerk Mugo developed when he started gaining more sense but still horrible in interactions, making the Elder mugo the "youngest" since it was the third and last iteration of Mugo, mature and learned. But this could just be me reading too much from a silly special chapter
I'm guessing the ages kinda do make sense if all three different personalities manifested at different times. Monster Mugo was probably the first and original personality making him the "oldest", Jerk Mugo developed when he started gaining more sense but still horrible in interactions, making the Elder mugo the "youngest" since it was the third and last iteration of Mugo, mature and learned. But this could just be me reading too much from a silly special chapter