Tight calves could be symptomatic of tightness elsewhere, especially if you are not running up hills.
Try stretching your glutes, hamstrings and the soles of your feet and check for pain / tightness. It may actually be there that the problem lies.
I usually run about three times a week also. More than that and I tend to have issues.
At 52 years old, my body just isn't up to the pounding of my youth. And I can't even party any more :-(
By the time things really get going all I want to do is curl up in bed and go to sleep hehe
I'm not really getting pain anywhere. We're a similar age and I think it's just wear and tear. I wouldn't want to give up my running just yet. I just wasn't into sport when I was young.
Fair enough. Take it easy and don't go too hard too fast (like I do) and your body will adapt. It's amazing just how much our bodies can change even when we are older. ;-)