Whether you are 8 or 80, or somewhere in between, moving your feet is a priority. It's something that coaches constantly harp on. Beginning kids often don't find it important, and so you have to drill it into them, and then they quickly pick up on it. Older players often find it difficult because of their age, but while age slows you down, it doesn't stop you from moving your feet – it's simply a habit. An older player who doesn't move fast but still moves his feet is faster than a really fast player who doesn't.
Here is Exhibit A, video of George Brathwaite (12:05) in a training session. George "The Chief" is well into his eighties (here's his Hall of Fame profile), but see how he still moves his feet? That's because he has made it a habit. Let me emphasize this again: Moving the feet is a habit. It has nothing to do with how fast your feet are or how old you are.
Often players instead reach for the ball, meaning they limit their range, go off balance, and have to do an awkward stroke instead of the one they've spent so much time perfecting. The problem is they haven't developed the reaction of stepping to the ball, and so they instead react by instead reaching – which both puts them off balance and forces them to improvise the shot. Just as a person reflexively blinks if something comes at their eye, you should learn to reflexively step to wherever the ball is going. This doesn't mean you'll reach the ball every time, and sometimes you might even take that step and still have to lunge after it, but that's only after taking that first reflexive step. Focus on balance, with your weight centered as you move, and only going to your back foot for weight transfer as you get into position.
Some would say, "Of course George can move his feet – he's a Hall of Fame player!" But that's backwards – he's a Hall of Famer because he worked hard to develop such basic habits as moving his feet. George can do it in his eighties. What's your excuse?