Why is the result 2 years, that would be one surely?
....also wouldn't you want D2 to be 2 not 14? I suggest you use this formula in D2 copied down
=DATEDIF(A2,B2,"YM")
For the whole period the answer would necessarily be an approximation because you aren't dealing with "real" months - try this version for C5
=DATEDIF(SUM(A2:A4),SUM(B2:B4),"y")
and similarly for the months and days in D5 and E5
=DATEDIF(SUM(A2:A4),SUM(B2:B4),"ym")
and
=DATEDIF(SUM(A2:A4),SUM(B2:B4),"md")
That gives a result of 1 year, 4 months, 0 days in total