Depends on how much space you want and/or need. We have been hosting for 2 years now in a 21 foot Class C and we are comfortable with it. When we first started out we took so much stuff with us that we thought we needed that each month we started to get rid of things we knew we wouldn't use. We also purchased one of those First Up Screen Houses which is where we set up our cooking area. As far as the age limit on the RV it depends on the park. We have been hosting at State Parks and there is no age limit. A lot of the private parks usually ask you to send a picture of your RV and yourselves. Hope this helps.
