John 14:8-14 (NIV) says:
⁸Philip said, “Lord, show us the Father and that will be enough for us.” ⁹Jesus answered: “Don’t you know me, Philip, even after I have been among you such a long time? Anyone who has seen me has seen the Father. How can you say, ‘Show us the Father’? ¹⁰Don’t you believe that I am in the Father, and that the Father is in me? The words I say to you I do not speak on my own authority. Rather, it is the Father, living in me, who is doing his work. ¹¹Believe me when I say that I am in the Father and the Father is in me; or at least believe on the evidence of the works themselves. ¹²Very truly I tell you, whoever believes in me will do the works I have been doing, and they will do even greater things than these, because I am going to the Father. ¹³And I will do whatever you ask in my name, so that the Father may be glorified in the Son. ¹⁴You may ask me for anything in my name, and I will do it.
Was the promise in verse 12 "whoever believes in me will do the works I have been doing, and they will do even greater things than these" only for the apostles or for Christians in all ages?
In regards to what I personally understand by 'works', in verse 11 Jesus gives us insight into what he means:
¹¹ Believe me when I say that I am in the Father and the Father is in me; or at least believe on the evidence of the works themselves.
Moreover, in Luke 7:20-23 (NIV) Jesus is even more explicit:
²⁰When the men came to Jesus, they said, “John the Baptist sent us to you to ask, ‘Are you the one who is to come, or should we expect someone else?’” ²¹At that very time Jesus cured many who had diseases, sicknesses and evil spirits, and gave sight to many who were blind. ²²So he replied to the messengers, “Go back and report to John what you have seen and heard: The blind receive sight, the lame walk, those who have leprosy are cleansed, the deaf hear, the dead are raised, and the good news is proclaimed to the poor. ²³Blessed is anyone who does not stumble on account of me.”
But feel free to justify a different interpretation of 'works' if you don't agree with this.
