Does a woman who breastfed me constitute a Mahram through fosterage, knowing that she gave birth to her last child four years before I was born, and I saw her breastfeeding another child when I was 18 years old?

A woman's milk establishes prohibitory fosterage, whether it is produced during pregnancy or not, or whether the woman is elderly. If the woman breastfeeds you with the prohibitory fosterage (five or more full sucklings), she becomes your foster mother, and her children become your foster siblings. The woman's children are permitted to see from you what a man is permitted to see from his unmarriageable kin (mahram (definition)) among women, provided there is no fear of temptation (fitna). Solitude and handshaking are also permissible with them under the same condition.