In 1979 I was 19 years old and had just started studying CS in community college. Through a lucky break I got a job at a consulting company and my first assignment was to write a 6502 macro assembler from scratch, in 6502 assembly language. At that point I had written less than 100 lines of 6502 code on my Apple ][, but I was fairly good with 8080 and IBM-370 assembly.
My mentor / manager outlined the basic model for the assembler and I wrote the entire thing myself, quickly getting it to the point where it could self-assemble, and adding features from there. I was making about $7 / hour when I started. However, I wrote a FORTRAN simulation of the hashing algorithm that I was asked to use, shared it with my manager, and got a raise to $8-something an hour.
I had macros, a very fancy listing format that showed all of the hex codes generated by the macros in neat rows, and a lot more. The entire thing fit on two tracks of the 8" floppy disks that we were using -- definitely less than 8000 bytes.
Oh yeah, we were in the same row!