If a man or woman becomes Muslim after
the age of thirty or thereabouts, do they have to be circumcised? Is a man who is not
circumcised permitted to lead the prayer?

Praise be to Allaah.

Circumcision is a part of sunan al-fitrah (actions befitting the
natural state of man) for men and women, but if it is not done after a person is
fully-grown, there is nothing to worry about. As for a non-circumcised man leading the
prayers, this is valid.