No matter what your workout routine, adding some gentle stretches will improve your flexibility and range of motion. You'll want to do stretches that focus on muscles you're working during the rest of your routine, but some general stretches in the morning and evening can be especially beneficial for seniors, since our muscles tend to lose flexibility as we age.
The National Institute on Aging recommends regularly stretching your neck, shoulders, upper arms, upper body, chest, back, ankles, legs, hips and calves. This might sound like a lot of stretching, but if you do a few stretching exercises each day, you can hit all of these areas fairly quickly.
You want to make sure you're doing stretches properly to avoid injury. Take it slowly, and never push yourself to the point of pain. You just want to feel a gentle pull on your muscle, and focus on taking slow, deep breaths as you hold your stretch.