Plenty of teenagers drive IS300's. In stock form the car is very forgiving and handles pretty well and isn't edgy. It's fast enough, but not super fast, so driven properly it should do just fine. It's got plenty of safety features such as brake assist, traction control, and skid control. In normal driving those features will never even come into play. The speedo/tach dial is now classic, as are the tail lights and the entire body style. Get one in really good shape and you can hardly go wrong.
PS: I bought my 02 when it was a year old, drove it for another two and a half years and never had a minute's trouble with it.