Age-related differences

 children
    Short attention spans - It’s a well-known fact that young learners have a shorter attention span than teenagers or adults, thus activities need to be changed regularly(each with a song or game to line-up in between). For example, each activity should have an average length of perhaps 5 – 15 minutes at most. Once you see the children are getting a little bored or distracted, move on to something new. These should keep them focused on each of the activities. It may sound like a lot to cover, but the more activities are changed, the more focused students will be.

teenagers
    Respond well to project work related to their personal interests - This age students have a great capacity for learning, enormous potential for creative thought and a passionate commitment to things which interest them. It is also connected with a  search  for  identity and  a  need  for  self-esteem. This is often the result of the students’ position within their peer group rather than being the consequence of teacher approval. All in all, project work seems to be the best tool for developing language skills through the personal evolution of the students, that's why the stage of lesson planning should involve a research on students' interests and careful thinking about the grouping(you need to know the personality of the students and their peer relationships)   
    
adults
    Discipline problems usually not an issue - Adults are often more disciplined 
than teenagers or children and apply themselves to the task of learning even  when it seems  fairly boring. They often have a clear understanding of why they are learning things, and can sustain their motivation by perceiving(and holding  on to) long-term learning goals. As to the lesson planning, there may be a problem with some activities, when learners need to participate physically(they don't really like that), although it's not actually misbehaviour in its original way.