With boas more then many snakes the condition of the female is a bigger concern then the age. They do need to be mature first but since the one in question is 13 that's not a issue. I had a female this year that produced a litter and feed only twice in almost 6 months. She went off food just before she ovulated and did not feed again until several weeks before she gave birth (132 days later). So the female must be in perfect shape in order to even survive the pregnancy let alone deliver a healthy litter. Breeding boas of any age has its risks. Females can and do become impacted with unfertilized ovum and if this happens they require immediate surgery to remove the impaction or it's fatal. This is not an often occurring issue but it does happen and you need to be aware of it if your going to consider breeding them.