In an older, now deleted answer to another question, it's been said that classical conditioning is a posited mechanism for fetish development. A bit more googling found a popsci article claiming something similar:
In the 1970s, scientists wanted to know if they could condition a sexual reflex in men. First they got volunteers and hooked them up to a device that measured tumescence. Then they showed the men slides. The sequence of slides was always the same - naked women, and then boots. Naked women, and then boots.
After some time, the scientists were pleased to see that the men responded to pictures of boots without ever seeing the naked women. Some of the men even showed response to sandals and high heels. They managed to instill fetishes in human beings. It would be interesting to see how deeply the fetishes "took." Was it specific to time and place, or did the scientists engineer a lifelong fetish in people?
But the article lacks further details on the studies (e.g. actual citations of the papers), and I do wonder if the studies withstood scrutiny over time (methodology, replication, etc.) There are good reasons to be bit skeptical of random "studies from the 1970s" in this area, e.g. see a related question on of mine on self-administered aversive therapy.
One 2004 review suggests that you can't "normalize" people this way (conditioning):
It should be noted that, as previously mentioned, there have been clinical treatments based on the notion of pairing a CS with masturbation to enhance responding to normative sexual stimuli, but with little long-term success (for review see Laws & Marshall, 1991b).
So that rather casts doubt of the conditioning theory of fetish development too, but are there more recent experiments arguing for it?