Longest time to complete a serious musical piece of work

Great musical ideas come and go, we all have different approaches to writing music...I am sure that some of us have grown as people as time passes, and the music may also evolve as well, stylistically etc...

Just for fun, and perhaps for some perspective for the younger members of the forum - what is the longest time frame that people have actually taken to complete a serious piece of music?

For me, it would be about 17 years.

I started a piano piece when I was roughly 17 years old, never quite finished it. Was initially written in a way that was inspired by typical pop music at the time that I was into. I revisited it around age 20 and added a bit more to it during a time in my life where I was listening to more progressive rock. 14 years later, around age 34 - I put the finishing touches and completed it, and it retained a slightly jazzier/sophisticated feel near the end of the piece.

The piece itself isn't anything that I would consider special, some 4 minutes long for solo piano.

17 years a long time, though I wouldn't say I struggled at all or was obsessed with the piece. I held the musical ideas in the my life as I aged, and it was fun to complete the musical idea when the time came due :)

What about you guys?

Great topic, @Grant Weep ! I am sure that @Henry Ng Tsz Kiu will be able to contribute to this topic given as how he always says that he writes his music over long periods of time.

My Variations on "Deck the Halls" for Piano and Orchestra I started writing the beginning of and the 1st and Rondo Variation back in the late 2000's and only finished it more recently in about 2023 I think. So about 15 years. And there are other old works that I have access to that I am in the process of finishing and publishing thanks to the fact that I can open all my old project files with Cakewalk Sonar DAW.

Thanks for your idea for this topic!