Is the truck 7 years old as well? The alternator should still be good, but it sounds like it's letting go.
The symptoms you're seeing (low voltage and charging system light) may be due to the alternator no longer supplying enough current to run the truck and charge the battery at the same time. If the alternator is not putting out enough power, the ignition system will start to draw power off of the battery.
Once the system senses a voltage drop, it kicks on the battery light. If the alternator is truely dieing, then the repeated deep discharges of the battery (without fully recharging it because the alternator is not putting out enough power) will prematurely ruin the battery. DO NOT WAIT FOR A TOTAL ALTERNATOR FAILURE!
First thing's first... I'd go to AutoZone and have the alternator tested. If that's the case, you can get a remanufactured alternator for a lot less than $250 while you're there.
EDIT: I don't know if a code is only thrown with a check engine light, but there may be a code with the flashing charging system light. Ask AutoZone to diagnose the flashing light. Your owner's manual may also tell you what a solid and a flashing charging system light are indicative of.
2003 Ford Ranger | FX4 Level II | 5-Speed Manual
A few minor mods... nothing cool enough to mention.