veterans
mounties ================ No, 'Mounties' are Canadian POLICE not soldiers. The word you are looking for is 'cavalry'.
horse soldiers
Troops
soldiers armed forces
Another word for not old is young.
Another word for a "number of soldiers" is "contingent." This term refers to a group of soldiers or troops that are part of a larger military force. Other synonyms include "troop," "unit," or "force," depending on the context.
cavalry
"Ancient" is another word for very old.
Another word for 40 year old is 4 decades. 8D
Platoon unit company division brigade army
Another word for an old female cat is a grimalkin.
old