As a matter of fact, with some external tools like MCEdit, it's not really as time consuming as it seems. A lot of large scale of Minecraft redstone contraptions are modular in nature, once you build and validate the basic idea, scaling up is just a matter of copy-pasting.

In my experience, the initial research/designing phase takes quite some hours (typically a good weekend), scaling up is must faster. In addition, most players who are into this typically have a number of creative worlds serve as libraries of past builds, so you'd almost never start from scratch.

Probably by being young and not having to waste it on bullshit things like earning money to buy food and shelter.