I'm 26 and my M3 arrives a few weeks after I turn 27. If you can afford the car, go for it! Before the M, I had a S2000 at 21.
2011 E90 M3 6mt AW/Speed Cloth - ZCP, Moonroof, non-iDrive - PCD 12/9/10
Painted reflectors, matte black grills/gills, RemoteKey+, Homelink retrofit, V1 Hardwire, GP Thunder 8500K, modmy3 LED interior, VRS Replica CF Front Lip, Dinan Mufflers, HRE P40 19" Satin Charcoal, Bridgestone S04