Unless you are a complete freak of nature or have the skin of a Wild Boar, It's gonna hurt. Basically it depends on the place where you get it. Everybody is sensitive on different places on his body.
Some people say it hurts most on the chest others say it's worse on the back.
It is never so bad that you can't stand it, you will never exactly know, unless you make that experience on your own. The amount of healing time required will vary from person to person depending on their health as well as the type and location of the tattoo, usually 7 - 10 days. Every tattoo, old or not, can be covered with something else. The only problem is to cover a tattoo that is already really dark, because the artist can't use a darker color to go over it. Sterilization is the most important thing in a tattoo studio.