at what age are the FelV and FIV tests accurate?

Doing a web search I come up with everything from they can be tested at any
time to it's not accurate till 6 mos. At what age do you usually test
kittens?

There are about 5 doctors at the veterinary practice I take my cats to. The
vet I usually deal with told me (last fall) he couldn't test kittens until
they were at least 12 wks. old. When I took the most recent litter up to be
checked (when they had diarrhea and weren't eating) I saw a different
(younger) vet who told me she could test them then (they were 2-3 wks old).
She did and the results were negative. She warned that there could be a
false positive at that age but if it was negative then they were negative.
The rescue group we're fostering for told me I shouldn't trust the results
because they were so young. So now I'm confused.

The kittens are now 7 weeks old and are itchy to get out of the cat play pen
I'm keeping them in. I don't want them interacting with my resident cats
unless I'm pretty sure they aren't positive. So do I need to get them
re-tested? Are they old enough yet?


Thanks

W