Well as 30+ myself i certainly knew my limitations in looks and how fucked i was in society from it when i was a teenager. I think to be incel isn't exclusive to any age range, but i would say that an incel at 18 would be double worse when they hit 30 just because of the deterioration that comes from age. Decay of an already ugly face is pretty much double game over, but this in itself doesn't stop an ugly guy who is a teen from being incel because such a person can't get sex just the same as the oldcels among us.
Mentalcels can still end up just as much of an incel they cannot get sex. It's a different boat but still leading to the same place.