To make sure I give you exactly what you need, could you clarify which of these you were interested in?

: Are you seeking advice or "white paper" style guides on strength training and muscle maintenance for women over 50 or 60?

It looks like your request for "proper paper: 'mature female muscle'" could refer to a few different things depending on what you're looking for.

: Are you looking for academic studies on muscle physiology , aging (sarcopenia) , or lipid dynamics in mature females (either human or in marine biology, like the Gulf Menhaden study )?

: Are you looking for information, articles, or profiles on mature female athletes and muscle maturity in the context of professional bodybuilding?