That's a difficult question to answer. Some aspects of technology haven't yet peaked or are developing at fantastic pace, others quit long ago. I will say that if I had to go back to a time period, I'd probably pick the early 1980s. There was still enough leftover from the vacuum era that it would be a cornucopia of devices to play with, but electronics was still discrete enough that a project didn't start with "Acquire an Arduino and load this sketch..." The only thing I'd really miss would be the powerful single-board computers of today.