I agree. At your age, you already have a very new, very desirable, and great car. Why lust after another car? The grass is always green on the other side.
ESPECIALLY at your age, regardless of whether you're making $50k/year, invest your money. The law of compound interest REALLY comes into play when you start saving at your age. Woud you rather spend a good chunk of your money on a car right now, or save as much as you can right now, retire when you're 50, and be a multi-millionaire?
If you are making roughly 50k/year and want to buy an M5, I assume you're financing it. If you already drive a 2007 335i, then financing another car, especially an M5 would be another unwise financial decision because you're literally throwing even more money down the drain. And cars are only as liquid as they are sellable. The depreciation you suffer makes it an unwise financial tool.
Be happy with what you have. I bought a 2002 330ci new, but really wanted an M3 but there was a year long waiting list at the time. Everytime I saw an M3 drive by, I was so tempted to trade in my car and get an M3, but then I would be taking a HUGE loss. Instead, I drove the car for 5 years, and now I own a 2007 335i as well. I love this car, and although there are greater and better cars out there, I am very satisfied and have no intention of lusting after another car for a long time.
I'm 24, have a full time job, own my car and home outright, and am continually saving. I could easily afford an M5 if I wanted to, but I'm not going to buy another car for probably another 5 years or until I'm married. Why? Because the discipline I have of saving now, will reap HUGE rewards in the future. I'm not taking a loss by driving a 335i, and neither are you.