I don't think there is such a thing as "too young".
Assuming you've left them with their Mom/Pack for a
reasonable 12 or so weeks, they'll have a full set of
teeth by then.
I wouldn't delay allowing them to start gnawing.
First, it may help direct them to chewing the right things, and...
regardless that they will replace those teeth eventually, having
good clean baby teeth are still important. IMHO.
