While waiting for the doctors appointment and picking out a bike, get the person to start an exercise routine of just walking. Doing this at a scheduled time every day will better prepare them for when they do get a bike and it will make the biking seem more fun. When I started, my doctor had me walk 1/4 mile the first day. That was to the end of my street and back. I cheated and went all the way around the block. 8 months later I did my first century.