The thing that ages software is changes. The irony with software is that the most successful pieces of software need to be changed frequently, because of changing requirements. It means that the software is very useful. The more useful it is, the faster it ages and the worse the code gets. The best written software that doesn't change means that its usefulness is very limited.

It is impossible to design software that can account for long term changes. It's 100% impossible. You need to design for the near future as best as you can, and realize that eventually you need to refactor.

So design your software with the best maintainability you can for the next few years and then try your best to refactor it as you go along with new changes, but don't beat yourself up with things like tech debt creep up.