Think about all the different documents that list an age for your relative. Can you use those to reach any consensus about when the person was born?
It is not easy, but can be done. Here is a link to several ages for an ancestor of mine and a chart I made to analyze his ages. Not the most professionally done chart, but it serves the purpose.
We’ll be devoting a whole issue of Casefile Clues in the future to working with ages, but this should be enough to get “Tip of the Day” readers started.
Just remember a secondary source isn’t necessarily wrong. In 1907 a widow testified as to who the siblings of her husband were. Did she know they were her husband’s siblings because she had first hand knowledge of their parentage? No. She had been told. Did she have reason to doubt it? Probably not. Was she wrong? Not likely in this case. She was suing her husband’s family and they stood to inherit some property. If she had provided an incomplete list of heirs, someone would have noticed. It’s not 100% proof she was right, but any source needs to be kept in context. Secondary just means that she didn’t have first hand knowledge of who her husband’s siblings were.