I'm 23 and my first car was a 1987 420sel MB. What a whale she was, but a fantastic car nonetheless. From there I moved onto a '03 1.8t A4. That car made me appreciate the "newness" factor you get from a fresh looking, younger-type of car. Finally I've found myself in an '05 M3, and this has been the perfect car to me.
I cannot imagine a better performing car unless some extra (EXTRA) money was involved. I came across the 135i about 6 weeks ago, and this car just makes sense to me. Tough to explain.
I'd love to put myself into antother M3, but the new price cannot be justified. A dealer expects an 80k tag on the new M3. I told him he could keep dreaming, but nowadays I don't think he'll be far off.
A new car is secondary to me at this point in my life. I hope to walk into a condo in the near future, and at $1150/sq. ft. for a 750 sq. ft. 1-bedroom that is no small task. The 135i fits the bill, as it won't be outrageously overpriced at ~35k, and satisfy's all that I'm looking for in a car.
I tend to agree with the OP. The 135i seems to be geared towards (and I hate to say it) high school seniors all the way up to the almost 30 crowd. Above that the 3-series comes into play. Somewhat subdued with performace, yet still great performance nonetheless, with added sophistication.