Kind of a pointless more on WA's part. If WA law says no one under 21 period, then those military under 21 with FL licenses would have to observe WA law when there. Regardless of state, you must observe the laws of the state you're in.
Also, FL does not honor "non"-resident permits. You must be a resident of the state whose permit you possess.
Also, FL does not honor "non"-resident permits. You must be a resident of the state whose permit you possess.