Lucky shiny?

I'm curious to know the odds of getting a lucky from a really old pokemon.

Not impossible, but not likely.

My spouse and I traded shiny Metagross, both traded for mon from August 2016, over 2 days. Both of us got 96% luckies. Lucky indeed.

If it helps the guaranteed (if either account had less than 10 luckies in the pokedex) mons to generate a lucky trade were from July or August 2016 (not September still so it seems they haven't updated that). It would be logical for any mon older than 2 years but it seems Niantic has just stuck to mons from those 2 first months of release. I would hold on to that last shiny until further research by the SilphRoad or clarification by Niantic is done, since lucky mechanics seems to be completely RNG at the moment

As far as I know, shiny pokemon have the same odds to become lucky as regular pokemon. I got 4 out of 4 lucky shiny metagross (100% of my trades). Used 3 old pokemon from July 2016 and one from October 2016 (the last was luckier than the others). You were only unlucky with your August 2016 pokemon, the other behaved as expected.

My shiny Gyarados and Dragonite can confirm shinies can go lucky. Outside of guaranteed rolls they're considerably less common due to the one a day limit on special trades.