I’ve always been into giants, tiny people and especially fairies, but I would pinpoint my “awakening” to M/f was Captain Planet S6E3, Frog Day Afternoon when Wheeler and Linka (who was my favourite character) are shrunk by Dr Blight. Wheeler reverts back to normal size first and has a brief but rather cheeky interaction with Linka. I’d have been around 5yo at that point.
I was exposed to sexual size content at around 15 or 16, but it made me uncomfortable and I had a complicated relationship with sex in general, let alone a fetish. I didn’t really get into it until I was maybe 20. I still very much have my preferences, but my tastes have changed over the years with regard to what I do and don’t tolerate.