Is it permissible for a man to marry his paternal aunt's daughter, who was also suckled by his paternal aunt, if he himself was suckled by the same paternal aunt?

If you and your paternal aunt's daughter were breastfed by your paternal aunt (your foster mother), then you become siblings through fosterage, and marriage between you is forbidden. This is based on the saying of the Prophet, peace be upon him: "What is forbidden by lineage is also forbidden by fosterage." The rule of thumb is that any two individuals who shared the same breast become siblings through fosterage. A condition for fosterage to prohibit marriage is that there must be five satisfying breastfeeds.