I have'nt seen the Rushen parish registers but the Lezayre parish registers typically did 
not record a birth date, but I have seen one or two birth dates mentioned. 
 Prior to 1849 entries were more or less written as a small paragraph with the 
following info: entry number, childs given name and parents names, date of 
baptism and often person performing the baptism.  for example:
128  Frederick  Son of John and Mary Christian
                (formerly Mylecraine)
                                  bapt. Feb 18 1849
                 by Edward Brailsford

After 1849 a standardized format was followed:
When Baptised- Childs Christian Name- Parents Name- Abode- Quality, Trade or Profession-
 By whom the ceremony was performed.  for example:
Feb   Francis   John  Christian   Sulby    
 14   Edward    Mary  Christian   Old      joiner   Benj.
492             Mylecraine        Village           Thompson   Chaplain

hope this helps.