Military papers usually record place of birth as the civil parish.
There are both Catholic and Church of Ireland parishes in Dublin city named St. Catherine's. Do you know what denomination this Boylan family were ?
Records for both St. Catherine's are on the free IrishGenealogy website, also if Patrick was born in 1864 or later then there should be a civil record of birth. This should provide his father's occupation, which could help confirm a link to the correct family (RC baptisms dont usually include occupations).
I had a quick search through the two St. Catherine's on the IrishGenealogy website but didnt spot anything likely for your Patrick. will check in more detail later on..