Do bosses scale to your level in Dark Souls?
Do bosses in Dark Souls scale to your level?
For example, fighting a certain boss at level 20 would be the same difficulty as fighting that same boss at level 50.
No, nothing scales to your level in Dark Souls.
For example, you can see the stats for the Taurus Demon here. It's HP is fixed - ie. not related to your own level.
Enemies do become stronger in New Game+ and beyond, but the increase in strength is not related to the player's level.