If you're browsing the Internet, emailing, using a personal spreadsheet, writing letters a computer that's 20 years old is just fine.  It's like my 21 year old car, I get 23 to30 MPG, I've been to Texas, I've been to California and all over Iowa &Illinois in comfort. 

If you're compiling programs, editing video, using CAD to make complex designs or playing MP video games you would benefit to have $3-$5K computer with lots of memory, an NVMe or M.2 drive.  Otherwise the computer I bought in 2008 still seems to work okay. 

I usually run my Lenovo with Window 7 desktop and find it to work about the same as my Windows 10 computer that has twice the memory.  Both have SSD's for drives.