The Grassy Gnoll
Explorer
Just had this exact thing; party level 5, newbie started level 3 so got the quick advancement up a level to level 4, giving them the thrill of levelling up and hitting a cool milestone level. So now is level 4, 1 below the others, who will be ahead of him unless there's a solo duel or something, but the player loved seeing the power leap rather than it being the 'norm'. In this case it was a total beginner to RPGs.