I started soloing MMs at level 14. You can solo Tough / High Def MMs with moderate difficulty. But there are a few rules that you'll need to follow to get maximumize your potential.
Buy the best bow for your level, which should be the Royal Archer Bow
Buy the best arrows, which should be the Iron Arrows
Wear your Ranger necklace that you get when you obtain the job class.
Start off every fight with Sharpshot, and you should be able to finish the fight in 6-7 shots if they all hit.. and most of them should.
Rest for 5 minutes, sharpshot is ready. Unless you have WHM sub, then you can try and risk it without Sharpshot.
If you get hit twice with Stonaga, get ready to run though. =)
If you have your 2 hour ready, you can even take down VTs, but you'd still only get 200xp.