GTA 3, so almost 10 years ago. 

I played the original back on the PSOne, but never really got into it until GTA3 on the PS2.
Didn't play the second game at all until more recently.

For me it was around San Andreas. I then picked up the PS2 trilogy and played through most of the games with that. Then GTA IV came along....

First GTA on PC, didn't play too much of it.  Then I heard GTA3 was coming to PS2, and I didn't know how big of a deal it might be.  I just thought 'maybe that will be cool'.  At that time I had traded my PS2 in and was only PC gaming.  I rebought a PS2 and GTA3 and I was amazed by it.  Played most of the GTAs since.

When Grand Theft Auto III released back in 2001.

Ok...I'm not proud of this but I guess it's time for me to be open about this but....
 

GTAIV was the first time I played a GTA game.

GTA 1 on the PS1 then every major GTA game since then

GTA 1 on pc and every other gta game that has come out since then

I played the original GTA on the PSX. I never understood why that game received such bad reviews. It was a ton of fun as far as I am concerned.

Played the Pre-release copy of the original on the PC 3 weeks before it shipped, and burnt out of the series by the second GTA 3.

GTA1 on PC, and almost every other after that.

My older brother went out and bought GTA1 on the PC way back when. He certainly wasn't 18 then by a longshot, so I might have been around 10 or even younger when I first played it. I don't think I really understood the mission structure, or at least wasn't too good for a long while, so I would just go on killing sprees. I needed cheats to access the other two cities.
 
He also borrowed GTA London a few years later. I still recognise songs from the soundtrack when I hear them and get all nostalgic.

Grand Theft Auto Liberty City Stories.

gta 3 ps2 completely hooked from the get-go

" When Grand Theft Auto III released back in 2001. "

Played GTA 3 back when i was like 9 or 10, we would just put in cheats and see how long we could survive with 5 stars

GTA 1. Then London got me really into it. Played everyone since,

GTA 1on pc.

I cant remember whether it was on PS1 or PC but I had both at some point way back when. I dont remember doing many missions though just driving like a mad man killing people lol

The first time I played GTA was when I was probably 6 or 7..... it was one of the PC games but I don't remember which one. So much fun.

I never touched the series before the 3rd one, and since the 3rd one I have been hooked on all the console versions.

GTA 1 was my first and that was about 1999 I first played it and thought it was the most amazing game ever.

Vice City hooked me first

The first GTA on the playstation. Then I went out and bought the gameboy version. I was about seven when I bought that. GTA 2 has the best mission system. I have played all of them except for London and Chinatown. 

GTA IV. had to really earn it from my parents. cause they hated that series with a passion

Oh, I first misread the topic and thought it said GTAIV. I was going to answer with March 29th, 2008. I believe that was the release date. Anyway, I believe I played one of the old top-down GTA games on PS1 long ago, but only for a couple minutes and never really got into it. Then came GTA3, which didn't hold my interest long. I wasn't crazy about the core game and getting into trouble and using cheats was only fun for so long. Then came Vice City, and man, even though GTA3 let me down, I was excited about it. I thought it was looking great and I was so excited that I even had my parents get it launch day for me while I was at school. It was going to be a birthday present. My PS2 had broke like a month or so before then, so I had it sent in for repairs, and it actually came back the day Vice City came out. So my parents let me play the gift early. I wasn't immediately blown away by it, but after getting over a few rough edges, I completely fell in love. It's my favorite GTA game and my 2nd favorite game of all time. I've been a huge GTA and Rockstar fan ever since.

Way back in 1998 with the first game in the series. Picked up the London packs too. Though I didnt really get into part 2 after playing it once or twice.  Since then I liked GTA 3, loved Vice City, ADORED San Andreas and mildly tolerated GTAIV. Such a disappointment for me.

I got GTA 1 for my PSone back in the day. Then i followed the series on PSone, but also got GTA 2 for PC when we got a 3D graphic card :)
 
I didn't get a PS2 until vice city had just come out, so i bought that straight away, but I still got to play GTA 3 at a later time. Since then I've played and loved them all. ;)

Bought PS 2 to play Vice City on release. That was the first I owned my slef, but I did play through the Very first and GTA 3. Never really got around to trying GTA 2. Huge fan of all the games until GTA IV wich in my opinion sucks tons of donkeyballs. 

GTA1 on PC

" GTA 3, so almost 10 years ago.  "

I started with GTA 1 on the PC, skipped GTA 2, never played London. GTA III is what made me get a PS2.

It was GTA 1 on PS1. My cousin used to borrow it from his friend, Command & Conquer Retaliation has changed my life. I think it was 1998 or 99.  
Then I was playing it A LOT on my first PC in 2000. Too bad GTA 3 was so resource hungry that i couldn't play on it at all. And again my cousin with his PC was there to help me play the first  Three-dimensional Grand Theft Auto. Good times, good times. 
 
PS. I was born in 1990. What? Age restrictions?