Age is an important thing. If your ancestor was not of legal age, he or she could not sign legal documents in his own name. Did a family wait until the youngest child was "of age" to settle up an estate?
Is the reason an ancestor waited to apply for military or widow's pension because they were not old enough or because the law changed, finally making them eligible?
There are age restrictions and other "qualifications" for a variety of things today. It's possible your ancestor had to "wait" until he or she qualified for something as well.