Of course, I'm totally crazy about the show.
The funny thing about this is that a "kid", of sorts, is the lead while all others are actors in their late 20s and 30s.
The kid is, technically, the same age as the others, but he time-shifted into the future for a while. Turns out, he was there 47 years or so. When he figured out how to time-shift back, he miscalculated and shifted into his teenaged body rather than one that reflected his real age.
Aidan Gallagher plays the character. In real life he is currently 19, but that is his Season 4 age until turns 20 in mid-September.