The game imposes a soft cap at level 50. Past level 50, leveling up happens much more slowly. The theoretical level cap (maximum level) is level 81, reached by increasing all skills to 100.(tested with player.advskill console cheat)
One implication of the leveling system is that although it is possible to create a character with 100 in all skills, it is not possible for one character to unlock all skill perks, unless a console command is used (player.addperk). In such a case, one may unlock every perk available, even at level 1. This, however, will disable obtainment of achievements, and is considered cheating. There are more than 250 total skill perks (including multi-point perks), but only around 80 of them can be unlocked by any given character."