I suppose that attraction to feet is more often around guys who wants be dominated. Since feet is the lowest part of human body, submissive man feels desire to bend over it, worship it, to show his devotion.
Earliest memories of FF of mine is when I was 5-6 and I was crushing ants stepping on them. It gave me some weird excitement but only if doing it barefoot.
Then when I was older I started pay attention to other boy's feet. A LOT. At 11 or 12 yo I expirienced first (and sadly, the only) FF practice with boy. We played "hypnotaze me and do whatever you want" game, friend rubbed my hair and face with his feet and managed to stick his toes in my mouth. I never been more aroused ever since, even when we fapped together.
Speaking of shotas, clearly it has to be a bucnh of submissive pedos who wants worship shota/loli feet and get exited about being subjected to someone young and weak. It's widespread over hetero men, why is has to be different here.