I got my first computer, a C64, when I was 14 in 1985, and wrote my 6510 assembly in paper as well.

You had to carefully calculate the address distance for a branch instruction. The release of DISMON was a revolution: suddenly the computer did all of that for you. It even supported moving pieces of code to a different address to make space for inserting more instructions somewhere!

All I had was computer manuals in 1981. I wrote several assembly language programs on paper.