This is the Certificate of Confirmation for Johannes:
Again, the first thing I noticed are the folds. Then we see his birthday stated as the 27th of the winter month of 1803. This just serves to tell us we are dealing with the right guy.
The certificate then tells us that Johannes received instruction in the Christian Evangelical-Reformed religion and as of Easter 1819, was allowed to partake of Holy Communion. He would have been 15 at that time.