First of all Malew and Rushen as two distinct parishes
2ndly earliest records at Malew are in 1650 (see http://www.ee.surrey.ac.uk/Contrib/manx/manxnb/v06p072.htm) and from Rushen an extremely late 1708 (presume a register has been lost)
see http://www.ee.surrey.ac.uk/Contrib/manx/famhist/genealgy/church.htm
thus these dates cannot be from parish registers - certain property records had birthyears but these are rare so my guess is that they were guesses