Father. We'd disassemble all our house bicycles each spring, clean and grease/lube all the bearings, tune everything. From about 10 years old I could do it most myself.
When bikes with speeds came, before I got Internet, I was in bit of a trouble. But I figured most things (like limit screws) on my own. With Internet and on-line downloadable PDF books and manuals, it's easy now. Sheldon Brown's site was also a great source.