Proline is not aromatic. While the ring does have 2+4n free electrons (from the nitrogen), the fact that the carbon adjacent to the nitrogen has three sigma bonds means that there is not an open pi orbital for electrons to resonate in.
This is not an aromatic compound because it didn't satisfy two of the rules for aromaticity. This ring has 4 double bonds, which means it has 8 electrons participating in pi bonding. According to...