You should try to exercise every day or at least 5 days/week. If you can't carve out a whole 30 min to an hour, try exercising for short periods, like 10 minutes each, several times/day.
While not having had a child may help your stomach skin tighten back up, it's not going to help the skin on your arms, legs, etc.
You can't lift and tone breast tissue, but you can strengthen and tone the muscles around the breasts. Exercises that are best are those that work the pectoral muscles. Do a search for "exercises to tighten breast muscles" and you'll find quite a few examples and/or videos to help you.