There are a variety of indoor activities for all ages available for people of all different ages. The precise nature of the activities that can be undertaken is generally determined by the amount of space and resources that are available. In theory at least if there was always enough space there would be many things that people could do inside. Some of the things that can be done are more passive in nature than others are.
People of all ages can take part in games and sports inside. There are more traditional activities such as playing card and board games, play musical instruments, or indoor sports. Many of these things have not been done so often since TV became popular, while computer and video games have become more popular than card or board games. However watching TV or playing video games is often blamed for people gaining weight so there is encouragement for people to start playing sports and been more active while they are inside. If there is enough room indoor activities include table tennis, basketball, table football / soccer and even yoga.