Your fine kid. If you're talking about matchmaking in the crucible, level doesn't matter. You do the same damage as anyone else. You'll die alot as everyone else has had the game alot longer and are just better players but you'll learn and get better. The boost that comes with the game moving you to level 25 is to allow you to skip the original destiny base game and start at the taken king expansion content (also referred to as year 2). It saves you from playing some of the worst content in the game.