I picked based off of box score last season and it worked out just fine...but I would only recommend doing it if you are picking between players who you don't know the potential and age of.
So...I had no 5 star players with 4 or 5 potential last season that were 18 yo. Instead, I picked the PG with 5 star rating and a ridiculous stat line. (37 points, 4 rebounds, 8 assists, 4 steals, 17-20 shooting, 2-5 3pt). I got a very solid PG, who was unfortunately 19 years old.
I think it is safe to assume that incredible stat lines come from good players as my player reflected his stat line very closely in his skills (respectable JS, mediocre JR, respectable PA, average PD). However, this is an isolated example, and I would always choose a 5 star, 4 potential, 18 yo with a crappy stat line over a 5 star, ? rating, ? age guy with a ridiculous stat line.
http://www.youtube.com/watch?v=oHg5SJYRHA0