Fallout games have always had a 20-level cap. This is the 3rd fallout game in the series. You'd expect its game mechanics to follow the other two, even if it is in 3d and not 2d isometric.
Wrong! None of the older Fallout games had a level cap. In Fallout the last new perks came available at level 18 and in Fallout 2 & Tactics last perks were at level 24. Of course you would run out of meaningful quests at around this time, but there was nothing stopping you from gaining experience or levels in random encounters or by slaughtering the whole ingame populace.
And it should be the law: If you use the word `paradigm' without knowing what the dictionary says it means, you go to jail. No exceptions. -- David Jones