Like GiC said, it tends to be more based on Spiritual maturity.
Communion with the Church is the most intimate form of interaction any human being can undertake. In Communion, we are united not only to Christ, but also to one another in a bond which is stronger than even blood ties or marriage. For this reason, the Bishop is responsible to ensure that those who are admitted to Communion will not betray Christ or His Body, the Church, later (as Judas did). Thus, before Communing, we pray:
"At Thy Mystical Supper, O Son of God, accept me today as a Communicant; for I will not speak of Thy Mysteries to Thine enemies, neither will I give Thee a kiss as did Judas; but like the Theif I will confess Thee: 'Remember me o Lord in Thy Kingdom.'"