Leveling up a pokemon early

i decided to make my growlithe at level 31 evolve, will the Arcanine it will produce be more stronger than a growlithe evolving at level 49?

Your Arcanine won't necesarily be stronger than if you had waited till your Growlithe was level 49, but it all depends on what area you want your pokemon to be stronger in. For example if you had left your Growlithe till level 49 before letting it evolve into Arcanine, then it wouldn't have had as much HP but it would have been faster and some aspects of your pokemon would be stronger, or weaker than what they are now.
Hope this helped