I haven't ridden anything "big" per se, but if it counts it was Scooby Doo's Ghoster Coaster at Paramount King's Dominion, if not then Big Thunder Mountain @ WDW, if that doesn't count, I got nothin
uh... OH, Space Mountain at Disneyland, the one where you went in circles six hundred times and the straight, and then another of six hundred circles. Scariest ride of my life, for a 7 year old.
So, my friend came up to me the other day and asked if I wanted a frozen banana, and I said no, but I want a normal banana later, so... yea.
Technically my first coasters were Thunder Mountain and Space Mountain at Disney World, but my first 'real' coaster was "The Beast" at King's Island, at age 7. The funny thing is that I didn't really understand the concept of what a roller coaster was at the time, so I assumed that it would just be like a Disney ride, with scary animatronic beasts jumping out at you in order to make the ride scary. Boy, I had no idea. It knocked my socks off. When we got back to the station, I was screaming "That was so awesome! I want to go again! YEAH!!!" and my mom was like "NOOOOOO!!!!"
My first "bigger" coaster was Temple of the Nighthawk in Phantasialand. Ow man, I was so scared! Completly dark and some weird ass science fiction lasers.
The first permanent coaster I rode was at Old Indiana, a small park that was about 15 minutes up 65 from Indianapolis. I don't remember the name of that coaster, but I do remember being terrified before riding. That park closed a decade ago and I'm pretty sure my first coaster is now scrap metal.
My first 'big' coaster experience was when my parents took us on a surprise trip to PKI, where we rode The Beast first, of course. I was blown away. The rest of the day at the park was fun, but we ended by grabbing a night ride on The Beast, which had a lot to do with why I became a roller coaster enthusiast.
I think mine was Vampire at La Ronde, but it's kind of hard to remember. It might have been Wicked Twister or something in Vancouver, not too sure though.
It could be one of three.....Polar Coaster at Storyland (I don't remember riding it but my parents think I did in 1994), Big Thunder Mountain at WDW (I have memories of riding this in 1995), or Yankee Cannonball at Canobie Lake (less likely as I'm not completely sure I went here until 1997, but there is a good chance I went in 1995 and 1996 too).
Hershey in 1999 was my first time at a "big" park and riding everything, but I didn't really care much about coasters beyond riding them at that point. Superman at SFNE in 2004 and then Boulder Dash in 2005 is what got me as interested as I am now.
My first ever roller coaster was Scooby Doo at King's Dominion at the age of 3, with Big Bad Wolf and Lochness Monster coming later that same year...my parents taking me to parks in Virginia as a kid is what got me into coasters...we went to BGE every Tuesday for like 5 years.
My first ever ride, at the age of 4, was the legendary Matterhorn Bobsleds at Disneyland CA. I feel that to be somewhat appropriate as I believe (and please do correct me on this) that it was the first ever steel roller coaster.
My first ever 'proper' roller coaster was Nemesis at Alton Towers, aged 8, which, let me tell you, was one heck of an induction to the roller coaster world.