I've had similar issues. I'm 45, 5'9" 175. I work out faithfully, jog, have great cardio, deadlift 400 pounds, squat 300 and bench 275. So I'm in decent shape. I play outfield, as well, and in recent years I've started getting very very sore after double headers, mostly in my feet and legs. I went to a sports medicine doctor, he told me I have flat feet and it messes everything up in the Achilles tendon and legs as you get older, particularly when you sprint. So I got better shoes, got some arch supports and the doc gave me a 15 minute warm up routine followed by 5 minutes of jogging before each game. My soreness is much better. The warm up routine is incredible. Its the warm up routine from P90x with some other dynamic warm ups like deep knee bends, single leg bench squats and bridges. It takes about 30 minutes in total. It really sucks that all the young guys just jump out of the car and start playing, and I have to get there 30 minutes early just to warm up, but that's life. As we get older, we have to work harder to stay competitive.