Aaron Hernandez -- Have Gun, Will Travel

Aaron Hernandez was locked and loaded 4 years before his current alleged murder predicament ... and he made sure to capture the gun-toting moment on camera.

TMZ has obtained this photo ... showing a 19-year-old Aaron brandishing a Glock handgun for a selfie iPhone pic. You can see a magazine inserted into the gun, but it's unclear if it was loaded.

We've learned the pic was taken in Gainesville, Florida in 2009 ... the same time Hernandez was playing football for the University of Florida.