You have to think more carefuly about your logic. Can you edit your question to explain what is your desired output and under what conditions?
0
=IF(
AND(
[@[Key Populations]]<>"Preg";
[@[Key Populations]]<>"BF";
[@Age]>14;
P135>='information Sheet'!$AD$2;
P135<='information Sheet'!$AE$2
); //Condition 1, OK
"VALID"; //OK
"INVALID"; // This should Condition 2
IF(
(OR(
[@[Key Populations]];"Preg"; //Should be [@[Key Populations]]="Preg"; I assume
[@[Key Populations]];"BF"; //Should be [@[Key Populations]]="BF"; I assume
[@Age]=<14;
P135>='information Sheet'!$AD$2;
P135<='information Sheet'!$AE$2
);
" ";
"False")))