A search on the WT library with the words 'approach mature sister' brought up 2 results, one from a KM which said a sister could approach another sister to give her opinion about her clothing.
The other comment was this from the W 1973 9/15. It is under the title 'Breaking free from SELF abuse'. Guess what the self-abuse is? Yep, masturbation. However it does set a precedent.
Some persons find it most difficult to discontinue the habit abruptly. So, when they occasionally relapse—usually in a state of semiconscious sleep—they develop deep feelings of guilt and of being unworthy of Jehovah’s mercy. For these reasons it is not only helpful but often advisable to seek the aid and encouragement of a Christian elder. When a girl has the problem she may want to approach either an elder or a mature, respected Christian sister for help.—Titus 2:2-4.
Titus 2:2-4 states
2 Let the aged men be moderate in habits, serious, sound in mind, healthy in faith, in love, in endurance. 3 Likewise let the aged women be reverent in behavior, not slanderous, neither enslaved to a lot of wine, teachers of what is good; 4 that they may recall the young women to their senses to love their husbands, to love their children
Seems to me that this supports teaching and shepherding in the congregation, but only between females.
Watchtower 91 7/1 states this
Our review of women mentioned in the Bible has enabled us to see that age does not prevent women of faith from serving Jehovah. This fact was illustrated in the cases of Sarah, Elizabeth, and Anna. Today, there are many Christian women advanced in years who are fine examples of faith and endurance. In addition, they can discreetly back up the elders by helping the younger sisters. Drawing on their long experience, they can give wise counsel to younger women, even as the Scriptures authorize them to do. (Titus 2:3-5)