Why not? When Wade was Rose's age, he was averaging 17 points a game in Conference USA. Because you can't just look at what guys did at the same age and say they're likely to improve at the same rate? Dwyane Wade didn't have a decent shot at being as good as Wade is now. No, you can't. But you can look at a lot of other factors and make an educated guess at how good at player might become. By the way, Rose's rookie year is really similar to Wade's. Per 36 minute stats.... Rose (age 20): 16.3 points, 6.1 assists, 3.8 rebounds, 2.5 turnovers, .516 TS%
Wade (age 22): 16.8 points, 4.1 assists, 4.7 rebounds, 3.3 turnovers, .530 TS% Given Rose's physical gifts, his work ethic and the fact the posted a very similar rookie season to Wade (slightly less efficient scorer; better distributor with fewer turnovers) despite being two years younger, it's fair to say he has a "decent" chance to be as good as Wade.