I have a bunch of 1:600 scratch built Napoleonic ships which were started by my late brother in 1969.
One complete, the rest just hulls with no masts or rigging.
I inherited them after he died 20 years ago.
I finally completed them about 10 years ago (and discovered why he hadn't - what a faff they were to make)
So that's just over 35 years; but he had them for most of that time.