gistfile1.cs

data = PersonHelper.SortPersonsByAge(data, Constants.MinAge, Constants.MaxAge);

// ....


        /// <summary>
        /// Sorts list of persons
        /// </summary>        
        public static List<Person> SortPersonsByAge(IList<Person> persons, int minAge, int maxAge)
        {
            List<Person> result = new List<Person>();            

            int iDelta = maxAge - minAge;
            if (iDelta > 0)
            {
                SortedDictionary<int, List<Person>> sorted = new SortedDictionary<int, List<Person>>();                                

                List<Person> tmp;
                foreach (var person in persons)
                {                     
                    if(sorted.ContainsKey(person.Age))
                    {
                        sorted[person.Age].Add(person);
                    }
                    else
                    {
                        tmp = new List<Person>();
                        tmp.Add(person);
                        sorted.Add(person.Age, tmp);
                    }                                       
                }

                foreach (var personList in sorted)
                {
                    result.AddRange(personList.Value);
                }
            }
            else
            {
                result = (List<Person>)persons;
            }

            return result;
        }