Good afternoon, sounds like we share the same car taste, as I'm also 18 as well. My first car was a 300SRT-8 and I absolutely loved the HP & torque... That being said, I was always looking for more in the interior. I bought my '06 SRT8 with 39k miles for $21k & drove it for a couple months & got bored with it.
Month or so after selling it, I was on Craigslist and found a local '02 745i with 154k miles, $12k. I decided to buy it because I knew I'd be just as happy in it as the 300, with cheaper payments too. I ended up selling the car with 164k miles, and only changed the oil, cabin air filters, and new tires
in my time of ownership (only sold because I wrecked it, plus it was getting quiiiite a few miles on it). But, I will say this; I definitely got lucky with my 745i (being it never had problems when I owned it).
What do I recommend?
Depends what you're looking for; 425HP, Ho-Hum interior, gas guzzler (another reason why I wasn't so sad to see mine go), not THAT spacious in the back for passengers, that you know may have some problems in the future (just like any other car).
Or, are you looking for a giant, luxurious boat (the 745), roomy, excellent interior, not fast (but definitely not slow!), that you know will probably have problems in the future that are gonna cost $$$.
Whatever you choose, goodluck!