Everything points to 20. The level requirement for all legendary and exotic gear is 20. There are also no story missions after level 20. (Earth has mission levels of 1-8, Moon has 6-11, Asteroid Belt 10-12, Venus 10-14, Mars 15-20) It will take much longer to level up than it did in the beta and there is end game content once you get to the cap. You can set strikes to have enemies of level 22, 24, 26, or 28 and the enemy levels go up to 31 if you put the vault of glass raid on hard.