Apostle means one who is sent. To “qualify” as an Apostle one had to be sent by the risen Lord to preach the Gospel. That is why St. Paul is an apostle even though he did not follow Jesus during His earthly ministry. The Apostles received their commission from Jesus after His resurrection (Matthew 28:19-20).
A disciple of Jesus is someone who is a follower of Jesus in his or her everyday life, i.e. a Christian.
