There is research that says we all have this kind of experience as infants or in the womb when the thalamus, the place where information from different senses is processed and sorted in our heads, is being formed, and for some people it continues in various forms throughout their lives.
It can be an advantage (seeing numbers in colours can make them easier to recall) or not (people don't understand you, the sensations can be overpowering sometimes). For more information about synesthesia check Wikipedia.
Rylie VanOrsdol is currently a sophomore in college with a 4.0 and will start college at age 15.