I'm 21, I've had the SDL since I was 18, wanted to buy one since I was 15. It was a combo of things for me. When I was growing up my dads friend would always take me on boats he was working on and show me the big diesels. I always thought they sounded cool, and were neat to look at. Then a Dr. that I know introduced me to his 300SD, which is currantly the same SD in my sig. I always thought MB's were cool cars and with a diesel I was sold. They were cheap and being a poor teenager at the time it was the only car I really liked that I could afford.
I like them a lot and am a die hard MB enthusiast. I probably won't always have a diesel Mercedes, but I will always drive Mercedes. They are the best cars in the world, almost anything else is going to be a down grade!