Honestly, if we take into account Elio's background: post-Graduation and the start of his Unovan journey, is Pokemon would easily be in the high 70s-80s. And if we do this on "Extreme Difficulty" or look at it as post-game boss fights, then his opponents would be about ten levels higher since they would use a team fit for higher-level challengers for a more balanced playing field; typically, it would also mean the implementation of more battle mechanics, such as field effects and Mega Evolution. This would give Elio's Pokemon a chance to level up. And that's not including the EXP candies he's won from tournaments on his journey and the various wild and trainer battles he's participated in. So, by the time he reaches the Pokemon League, his level cap is maxed out.

Buuuuut~ depending on the region he traverses, his Pokemon's level cap will increase again. Such as the Aevium region (Pokemon Rejuvenation) or Omuran/Deshret (Pokemon Empyrean), hypothetically of course. Regardless, gameplay wise, by the end of his journey, his Pokemon would be at the "peak" of their power.