I started keeping a simple spreadsheet in 1995...
It has evolved into a less simple (but not particularly sophisticated) XL file that plots daily mileage, Year to Date, corresponding date last year, which bike, chain life, Audax distance and a couple of other things. All quite useful, particularly plotting time and average speed over the same rides and comparing them with previous years.
We've moved from Perth, to Sydney, and to 3 different addresses in Brisbane during that time though so I can't directly compare performance this year against 18 years ago.
On the other hand, I don't need a spreadsheet to see the hand of time is beginning to pull on the back of my jersey....