What are some decent new(ish) cars you can buy that have an old school feel?

You pretty much just described an e30. Better get good at repairing head gaskets and chasing electrical gremlins though

When I was 16, I found a beautiful red M3 e30 for $15,000 and tried to convince my dad it would be a good investment.
He laughed at me saying used cars weren't investments. THEY GO FOR OVER $50K TODAY DAD. NOW WHO'S LAUGHING? (Well not me, I'm not laughing. I drive a scooter at the moment. Feels bad man)

Any good cars less than 15 years old that could be a decent substitute?

Might go check this one out: autotrader.co.uk/classified/advert/201712312359627
Looks clean, original, service history stamps, and no fucking shitskin drug dealer rims/tinted windows/douchy interior

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That's also implying that you, the 16 year old would not have fucked it up in any way, shape or form.

And being 16 once/knowing 16 year olds points to....bad

That's also what I was thinking to myself. There's no way that car would be worth >$50k if I had driven it at 16.

Also considering this one:
autotrader.co.uk/classified/advert/201801303226656

It is a sportswagon BUT it has the engine I want and the interior is giving me a boner

Mazda if you're poor