Here we don't deworm at any certain age.
I have 6 kids who haven't been dewormed yet (4-5 mo. age range) because it's been so very hot and dry here and they haven't needed it.
Having years of experience helps me to know when they need it....I keep an eye on their coat, behavior, and eyelid color. If I see one (kid or adult) looking 'off', I'll have a fecal ran by the vet, so I know what parasite they have. Some wormers are more broad-spectram than others, some don't work at all in some areas (from overuse) and some won't work at all on certain things.
If you just randomly give them dewormer w/out knowing if they need it, you're asking for resistance issues. Sort of like taking antibiotics when you don't need them...they may not work when you do.
IMHO, one of the no. 1 reasons people lose goats and get out of goats is because they improperly manage parasite issues.
Yes, it's a lot of info and it's a lot easier to "just deworm them"....but that's how "we" (goat producers) got into this mess we're in now.....by doing the simple (and wrong) things.