The first procedurally-generated ELW I found was, of course, already found and tagged by someone else: Wregoe AK-C c27-7, planet 1. I took pictures of it anyway, because I'd never found such a thing before.
That was in December 3301/2015, about 5 months after I started playing. Yes, it took me 5 months between starting the game and getting enough credits to buy an Asp to do some proper exploring. Historical note: as you can see, this was an early iteration of the system map: the planet-selector cursor is square, and the planet's vital statistics are missing a few key indicators... such as surface gravity. You'll also see it was before ship-names were an option, as my Asp has neither name nor ID plate.
The first ELW I actually got to put my tag on was Bleae Thua MX-B d13-8 A7, over a month later, by which time Horizons had been released: the planet-selector had evolved to its present circular shape, the surface gravity is now included in the stats, and airless moons have the "landable" crescent:
And just you show all you whippersnappers what life was like back then, here's the screenshot I grabbed of the awesome 50% bonus I gained for scanning this wonderful planet:
Yep, that planet bagged me almost an entire 100,000 credits. Even back then, that wasn't much to write home about, you could easily get more than that by blowing up a few pirates.