What Causes Extreme Calf Pain In An Elderly?

Male 86 yr old....has extreme pain in calf of legs, says when standing feels like pressure pain pushing down on leg., also has lighter pain in buttock area. Leg slightly swollen, skin cool to touch in spots (at times) otherwise is warm, legs are not discolored... when I massage the area it is hurts and can feel swollen area approx. 1 inch wide and several inches long?