I would be cautious about using naming conventions as definitive evidence - not every family followed these, and even when they did there are various factors that can alter the pattern, e.g. both father’s being the same name, a child dying young and name reused, a beloved family relation dying and their name used to honor them.
It was very common for people to mis-report their ages/years of birth, so I believe a 1817 baptism is certainly within the correct timeframe. The only slight difficulty is the parish where the baptism you mentioned took place St. Nicholas, Francis Street, Merrion Square is to the east with a few parishes inbetween and would have been in St. Andrew's Catholic Parish. The parish church is now on Westland Row, but back then it was located on Townsend Street.