Take a classic lugged steel road bike that survived well from the mid 80's. That is a ~20 years! Simplify the drivetrain. Adapt the rear wheel through retensioning and redishing. Overhaul Bottom Bracket, Headset, and both hubs. Use a new fixed cog, and new chain with fresh rubber and wrap and BAM! Now it is ready for another 20 years.
Here is the Red Fuji finished.