Explanation:

People: M, N, O, P, Q, R, S and T. Ages: 8, 12, 14, 21, 28, 36, 44 and 56. 1) Either T or the one whose age is 56 years is sitting at the extreme end. The one who is 56 years old is not sitting to the left of T. 2) One person is sitting between T and the one whose age is 56 years. 3) Two people are sitting between O and the one whose age is 56 years. 4) The one whose age is 14 years is sitting second to the left of O. 5) N is sitting to the immediate left of the one whose age is 56 years. (Hence, there will be two possible cases)
 
6) There is a difference of 6 years between the ages of R and S and two people are sitting between them. (The condition which satisfies the age difference of 6 years is only 14 & 21 and the position of the one who is 14 years
old is fixed and it is also given that either R or S is 14 or 21 years old. Hence, case II will be eliminated as T cannot be 21 years old). (Further from case I, there will be another two possible cases)
 
7) The one whose age is 12 years is sitting second to the left of P. P is not sitting at the extreme end.
 
8) There is one people sitting between R and the one whose age is 44 years. 9) M is an immediate neighbor of the one whose age is 44 years. (Hence, Case I will be eliminated) 10) Q and the one whose age is 21 years are immediate neighbors. 11) T is older than M and N is younger than Q.
 
Clearly, the age difference between M and S is 13 years old.