YoungGroup (<20 y old):
    Person1Name, Age
    Person4Name, Age
    Person3Name, Age
AdultGroup (20> y <40 old):
    Person2Name, Age
    Person7Name, Age
    Person5Name, Age
SeniorGroup (40> y old):
    Person6Name, Age
    Person8Name, Age
    Person9Name, Age

var multiplegrps = from p in people
                   group p by p.Age into groups
                   let age = groups.Key
                   select new
                   {
                       YoungGroup = from p in groups
                                    where age <= 20
                                    group p by p.Age,
                       AdultGroup = from p in groups
                                    where age >= 21 && age <= 40
                                    group p by p.Age,
                      SeniorGroup = from p in groups
                                    where age >= 41
                                    group p by p.Age
                   };