I make it 1970 (2013-43), not only predating vim by 21 years but actually coming six years before vi itself - an impressive degree of prescience in anybody's book. And this achievement is rendered all the more impressive by - assuming my internet searching and between-line reading is up to scratch - coming a likely 6-8 years before its author was even born.
I don't think it's actually that old. A lot of plugins from the vim-scripts' GitHub account have a similar date, like this one: https://github.com/vim-scripts/a.vim.