In the 'Hunter x Hunter' series, the character of Hisoka is quite complex and polarizing. He's not a typical villain or hero. His most striking trait is his pleasure in seeking out and battling against formidable adversaries. He thrives on the thrill of the fight and the anticipation of a tough challenge. This is why he spares potential strong opponents - all for the promise of a more exciting battle in the future.
Now, his interest in strong fighters regardless of their age could certainly come across as unsettling. He exhibits a strange sort of excitement when facing off against them. However, labeling his fascination and excitement as perversion might be too simplistic. It's more akin to bloodlust or a warlike instinct, matched with a wildly unorthodox moral compass. He is a character that walks on a different path, one that doesn't comply with the standard rules and norms, which makes him all the more intriguing.
In conclusion, the answer depends heavily on personal interpretation. While some see his actions and motivations as perverse due to their intensity and fixation on strength, others view Hisoka as simply a twisted antihero with an unorthodox set of values. Hisoka's character is painted in shades of grey, intentionally designed to confound, provoke, and intrigue viewers. And in that, it undeniably excites.