(split in two due to size restrictions ...)
Yes it's fun too after 30 years, I still get a ton of pleasure when I write something that works. There's the pleasure in figuring it all out, the creativity in your architecture and design, and the immediate feedback in seeing it alive in the real world. Nothing else I've seen gives as much.
"The main mistake I made as a teenager was wondering if programming was the right choice, instead of just coding something."
A common problem I see across the N-S spectrum, and one I've had too. Too easy to endlessly speculate about what to do rather than just do something. The opposite is somwhwat mindlessly doing something without knowing why or if it's worth doing, but few INTP's suffer from that.
On getting started, people constantly fret over 'how to start'. I want to laugh, the question really is 'how can you not start?' There are a million resources.