Sheikh al-Sharîf Hamzah al-Fa`r, professor at Umm al-Qurâ University
Yes, she may cast aside her outer garment in the presence of non-mahram men but she should still avoid being alone with them. However, it would be better for her to continue wearing her outer garment.
Allah says: “Such elderly women as are past the prospect of marriage. There is no blame on them if they lay aside their (outer) garments, provided they make not a wanton display of their beauty: but it is best for them to be modest: and Allah is One Who sees and knows all things” [Sûrah al-Nûr: 60]
There is no specific age for this ruling. What is important is that the woman has reached an age where she feels no desire for men and men who look upon her feel no desire for her.
And Allah knows best.
Source: Islam Today