I am the same way before getting new animals, and believe it's a very good investment.

We have raised ours strictly for 4H & pets up until recently. Now we're breeding and raising for 4H and for market. The rule of thumb that has been taught to us is more weight than age. Although, if taken care of properly, the age will be consistent with the goats reaching that weight. We shoot for 50 lbs.+ Which tends to be around 5-6 months. Good luck, and if you have any more questions about it please feel free to contact me. If I don't know then I'll certainly ask my "mentors" they're long time Boer breeders.