This makes me realize The Sims 3 has been around for over half of the life of the series. I mean, that actually makes sense since there's four of them, so assuming roughly equal time, it should have been around for half. Since The Sims 4 has had an unusually long life, it's been longer. It just feels strange since The Sims 3 still feels "current" in a way whereas The Sims 2 or especially The Sims 1 feel more legacy. But I'm wondering how much of that is down to me having not moved to The Sims 4.
Anyway... I can't remember the exact time I got into it. It would have been around the mid-2000s though, and it would have initially been with The Sims Complete Collection. A friend had a sister who owned it and she brought it over. Upon my reaction, she also had The Sims 2 base game (which I think was still relatively new) and brought it over. The only thing I remember from this was her being surprised it ran better on my PC than on their family PC. Theirs was newer than mine (If I had to guess, it had a Pentium 4 and I still had one with a Pentium III) but mine had a video card and maybe some more RAM which is probably why it ran better since The Sims 2 was 3D. Going on what I recall from when I replaced that PC as well as when the Sims 2 released in 2004, I'm going to guess it was around 2006-ish when I first played the series. Though, I knew about it long before. I was mostly playing Sims City 2000 back then.
She ended up giving me their copy of The Sims Complete Collection since her sister moved out or went to college or something (which I lost and am sad and wish EA made it available digitally) and my friend was more interested in The Sims 2. I also ended up getting The Sims 2 Double Deluxe via the now defunct Direct-2-Drive digital store in late 2000 since I liked what little I tried of The Sims 2 as well, though I never invested much time into it. The Sims 3 was inbound so I wanted for it, got in 2009, and... I've been stuck there on and off since.
I wish the Sims 1 and 2 were available digitally via EA though. I still have the digital copy of Sims 2 Double Deluxe but I'd probably get the expansion content if it were all available digitally.