based on my 5 box team in RFC, I would say that you could take a shot at RFC at 16, but:

  • Be very carefull
  • Make sure you bring LOTS of water as you'll be drinking after every pull in some places
  • Bring pots and food to increase your hp for the big fights
  • Be patient, clearing with 3 will be slow

But other than that, I think you can do it for RFC and the loot would still be viable, but the slowness of the kills probably means that it's worth doing once or twice for fun, quests and some loot - then questing is quicker xp.