Slash has got to be older... He still kept his speed. It's lack of practice time as we age.. Don't blame age. Also if you do heavy lifting your muscles will become tight. It's important to stretch the fingers so they are completely relaxed. Any tension in the body will take away from speed. Also breathing is important. Holding the breath causing tension and a rise in blood pressure. To perform at high speeds relaxation of the mind and body is critical. I haven't lost any speed a 53. I still lift, do cardio, stretch and play the guitar. I also am considering adding in 15 min a day of Yoga to help be in the present moment. Speed comes from muscle memory .. You must never rely on thinking unless your LEARNING a new piece of music. There should be no thinking of where your fingers go, what comes next, which footswitch to press. It should all be practiced so many times that the cortex of the brain is free to think of the big picture not the small hand and foot movements. It's just like driving a car . When you first learn you think press the brakes to stop, the accelerator to go, put on your signals, check your blindspot. When you get experienced that's all muscle memory (which seems like speed). Your mind no longer thinks of these things but the big picture. Which is the fastest route? What are the weather conditions? etc. Keep practicing!
dsouza
www.AdrianDsouzaRocks.com