Do you roll your feet when you walk or do you just plant your feet (stomp basically, you may not notice, ask others in your home if they think you "Walk Loudly"). Remember to bend your knees a little when you walk.

Don’t sit in one position too long, when you are uncomfortable, its your body’s way of telling you to move a little.

I am 20 yr old with flat feet to, I spend plenty of time at the computer, the only times I have back pain is when I accidentally lift with my back or when I am working with lots of oiled up metal (it seeps in my skin and causes general Joint stiffness which leads to pain).