Warren, This past season I believe that NSA allowed metal at 16u, ASA did not (maybe it was the other way around) But this year 16u is allowed in ASA.
BUT I bought a pair that we could change the spikes so my daughter could try them out before putting alot of money into a better brand. She prefers the "non-metal" but I can't find a pair that the spikes last a full season (summer only, let alone a full 12 months)
Some players like metal, some do not. Have heard pros and cons on both.