I first played TF2 on Xbox 360, bought Orange Box with some birthday money around late 2007/early 2008 when I was about 11.
Got into competitive after about 1000 hours of spamming pyro on The Rabbit Hole pubs (not a furry server btw) via some Facepunch thread that some guy wanted to make a CEVO S6/S7 team (original CEVO run, not the reboot). I had played a bit of tf2lobbies.com and seen some Extine casts on CommFT (first one I remember was MuscleMilk v Complexity in S5 of CEVO I think?). Our "tryouts" consisted of playing 3v3 pubs and spamming scout 1v1s on dm_duel2.
Eventually I ended up making my own team with a super edgy team name (again I was like 13~ at this point give me a break). We won our first pre-season game where I played heavy weapons guy the whole time on Ashville. We also eventually lost a game that was 6v5 on Prolane to skyhigh because we accidentally had 2 demomen for a round (thanks Cash50).
After that I ended up trying to make a few teams work and played a few ESEA matches here and there but was never really successful because I was dropping like legit sub-100 dpm games on the regular, but there were no logs outside of ESEA so I could hide it by being a cap points and post-round kills merchant. 
My most memorable match was this one because I subbed for the other team previously but they promoted a different player to be their main scout: https://play.esea.net/match/2091646
To be fair, they probably made the right choice since I dropped a fat 13-25 KD, and the player they picked was Tagg, who apparently, ended up being pretty good. 
I ended up quitting because Vhalin was offering mentoring on the CommFT forum and he said his only actual advice is to get a 120hz monitor, which I couldn't afford cause I was like 14 still so I gave up until I got my first real post-college job at 22. On one hand, I do kind of wish I had the money and resources to keep playing back when I was 14, but on the other hand since coming back, I'm pretty happy with the experiences I've had, and I'm sure things wouldn't have turned out quite the same if I had kept playing back then. 
I'll add also though, I think this is something that the whole time I had still wanted to do, but just never had the chance until I had the money. After I got a good computer and monitor for the first time, this old ass game was the first thing I was excited to play, 8 years later.
Other random thoughts/memories:
-I thought it was cool seeing how many random low to mid level players ended up being great players by the time I returned. Seeing what all had happened since I quit was like I had stepped into a time machine. I remember we rang Starkie for an ESEA open match and I didn't know who he was. I unironically asked our player who suggested we get him to sub for a match, "is he good?".  I also remember making fun of remix (aka dflame), mustardoverlord, ninjanick, and marmaduke, who all ended up being good players (also were much better than me at the time already, like I said I was dropping double digit DPMs on the regular). Also, in the same vein, I remember seeing Reckful (RIP) on tf2lobbies occasionally, he was already a top WoW player but he hadn't really gotten gigantic in the streaming world at the time. At first I thought he was just some Complexity fanboy since he had the coL tag but I had never heard of him.
-Funny gotfrag dramas including the dawn of MyGamingEdge, "Smoke a Victory Blunt", the TLR trophy incident, and eventually, the whole site being nuked
-Playing the first ETF2L HL tourney on dog ass ping to get the medal (first one they added to the game I think?)
-Chilling in the old Apocalypse Gaming Mumble server, shoutout Nahanni, meo, and Jeff Walters (athough Jeff ended up being extraordinarily racist, I found out later)
-I offered to make a frag vid for another Open team I subbed for, but my shitty computer couldn't render fast enough so I ended up giving up on it. I put some of the unused clips I managed to render in a frag vid this year though.
-Ehfk's Equalizer frag movie is still my favorite one, it was made back when the Equalizer gave both speed and damage, and had max damage > 150: https://www.youtube.com/watch?v=QAlzSCCTIhs