In Holy Scripture, Acts 1 25-26 Matthias take Judas’ apostolic ministry.the qualifications for bishops, priests and deacons are outlined in 1 Tim, 3:1, 8 and 5:17
St. Paul is considered an Apostle because he was chosen by Our Lord.
The end of the Apostolic Age is considered to be marked by the death of St. John.
After that we - and all who followed the Apostles- become disciples of Christ…
does that help?