According to Scripture, it's most definitely an office:
Acts 1:20
For it is written in the book of Psalms, `Let his
habitation become desolate,
and let there be no one to live in it';
and `His office let another take.'
Timothy 1:3
"A faithful saying: if a man desire the office of a bishop, he desireth a good work."
The Apostles - the Twelve, then Matthias and Paul - were explicitly differentiated from the 72 disciples sent out by Jesus. They were referred to by different title: Apostle or Disciple.
Selecting ONE human on earth to be "THE" apostle is silly..
We will have to disagree, given the Church's interpretation of the naming of Peter and the handing of the keys to the kingdom.
True...