Suggestions abt different stage formula milk

Hello mommies .. I accidentally bought 6 to 12yrs formula milk instead of stage 4.. n I hv used since 10days n lately I hv realised tht I bought over age formula milk .. My question is : is it ok to use for my 3+yr boy or am I need to stop it , after using it he got caugh n cold badly with phlum .. is it bcz of it or not concern abt it , pls suggest thx