=IF(DATEDIF(A1, B1, "D")>365, QUOTIENT(DATEDIF(A1, B1, "D"), 365)&" year(s) "&
QUOTIENT(MOD(DATEDIF(A1, B1, "D"), 365), 30)&" month(s) "&
MOD(QUOTIENT(MOD(DATEDIF(A1, B1, "D"), 365), 30), 30)&" day(s)",
IF(DATEDIF(A1, B1, "D")>30, QUOTIENT(DATEDIF(A1, B1, "D"), 30)&" month(s) "&
MOD(DATEDIF(A1, B1, "D"), 30)&" day(s)",
DATEDIF(A1, B1, "D")&" day(s)"))