I started Y in Oct 2013 and found my first shiny, since Gyarados in Crystal, on Mar 3, 2016. It was a random encounter, I was in Lost Hotel looking for a Magneton to breed with my other Megneton for Magnemite for my National Dex. Didn't know that when the guy says "Don't seem to get along" they can still have an egg. Ditto and others usually got that message. Ran into 10 Pawniards and left, changed my mind on leaving and ran back in and it was the first encounter.
My second was a Geodude in a hoard in Victory Road, I did about 10 sweet scents and found it on Mar 24th.
My 3rd was my first fish chain shiny, I went to the middle of the lake and got 97 reels in and found Corsola. I definitely now find areas close to edges but that luckily worked. I also found 2 Basculin looking for Poliwhirl.
The next day on the 26th I fish chained 6 shinies, first Goldeen at 20, then Corphish at 17, then Magikarp at 7. After was Corphish at 30, then Magikarp at 23 and finally Goldeen at 37.
The next day, found Poliwag at 56. Had previously gone over 100 encounters looking for Poliwhirl twice.
On the 31st I found a second Geodude, this was a random encounter.
On April 10th I did my first Friend Safari shiny hunt, found Phantump at about 100
Then on the 16th found Teddiursa at 210
On the 17th found Ponyta at 42
On the 18th found Meinfoo at 45
On the 25th I decided to use my Y in my 2DS and was able to enter my friend safari as Y was connected to my 3DS. Found a Venomoth for my national dex and was riding towards to exit and had one final encounter and it was shiny Venomoth. Maybe 12 encounters.
There's been 2 incidences where I hit the A button during fish chaining without hearing or seeing the mark/ding and a fish catching the line at the exact moment, theyby not breaking the chain. Neither of these lead to shinies. Mostly just muscle memory and luck.