Is buying my dream car at 18 dumb?

I recently turned 18. l'm a european car technician and I make $20/h. I also door dash on the side for and extra ~$500/mo. I use my friends tesla and split the income, so I’m not spending any money on gas.

I have 3 cars: A 2009 honda civic with 200k miles, a 2008 audi tt 3.2L with 99k miles, and a 2010 bmw 3 series with 142k miles. Insuring all of these cars costs me roughly $400/mo. I'm still living with my parents so I have no other expenses. My dream car, a bmw f32 435i msport, would run me $15k to $20k with like 70k miles.

I don't need 3 cars. I want to sell the audi and honda. The audi could fetch nearly $10k and the civic maybe $4k on a nice day. I've got $2k in a brokerage and $2k in checking. l've also got like $20k worth of watches, golf equipment, car parts, and electronics. Being less liquid, I would only really fall back on these during tough times.

If I sell the two cars, I could buy my dream car cash at 18 years old. I would keep it through college. I would likely not sell my current bmw, as it's extremely modified and has very high sentimental value.

I know spending $20k cash on a car at 18 is not smart, but I keep finding myself saying "you only live once" or "the money will come back but l'll never be 18 with my dream car again"

Help reel me back in if I’m being stupid