If you are bone stock, a 1/4 mile e.t. of low to mid 13 seconds is average. If you can break into the upper 12 second bracket your driving and your car is above average.
Mid 13s?? That's quite high. That's with a driver that needs to practice...a lot.
Edit!! Scratch that, was thinking of the Boss. Oops
OP, You have to realize, the published numbers from reviews are always coming from either pro drivers or drivers or extremely good drivers that have been driving for many, many years. You know which cars are the most deceiving when it comes to 0-60s and quarter miles? Higher hp AWD cars, like the STi etc. Those guys will rev high, dump the clutches and launch the car so hard, that if you were to do it, you would destroy the clutch in a matter of months. For instance, my Audi S4 was supposed to be around 5.2 seconds. I couldn't break 5.6 because any harder would have surely fried my clutch.
The mustang GT 0-60 is about 4.5 seconds, according to the reviews and Ford. If you can hit 4.8, you're doing well. At 5 seconds, you're making some progress. Keep at it, you'll get better. Just remember, it could be worse. You could be driving an AWD car that you have to fry the clutch to get good numbers lol
2014 GT White Premium, 3.73s, ROUSH phase 1 Supercharger, True Forged Mach 5 wheels
2014 F150 Phase 2 ROUSH supercher kit, leveled, Hostile Hammered wheels