Not necessarily! Look at the Blade series! Both 1 and 2 are certificate 18 and they still made some more and in my opinion Blade is an excellent film! Blade 2's alright! But theres no reason why it wont be 18! -A- (Unless im behind the times )
from what I have heard the rock is no long staring in this film as the lead marine, from what I saw in pc gamer and on IMDB its now Karl Urban who had the lead role ... he bin in such films as lord of the rings, chronicles of riddick, the bourne supremcy, ghost ship and was in xena warrior princess more then often tbh I think he will be a better marine then the rock would ever be http://www.imdb.com/title/tt0419706/