Is it permissible to pay the Zakat on camels by purchasing the obligated age (of camel) from outside the herd, while it is present within the herd, in order to avoid paying it from among the younger camels (qala’is al-ibil)?

There is no harm in paying zakat from money other than the money on which zakat is due, and you are not required to pay zakat from the exact money itself. This is permissible because it is allowed to pay zakat from other than the exact money on which zakat is due, and because the matter of zakat is based on facilitation and leniency.