I agree on the minimum level. If you are going with a group of friends, do whatever you want but if you are going to try to join a random group you should be high level. You can get to 28 just doing your vanguard, crucible or faction rep and buying a full set of legendary armor. Additionally, you should be able to pretty easily buy a piece of exotic gear from Xur and that with 3 pieces of legendary gear gets you to 29. You can do all of this within 3-4 weeks of hitting level 20. When someone who is level 26 is looking for a VoG group it just tells me they can't be bothered to spend a few more weeks gearing up.