I've known people who left their ps3 on 24/7 for more than a year
PS3s only overheat under specific conditions when they're not ventilated well
as for YLOD is not really an overheating issue....but more of the thermal paste on the motherboard eroding away, yes overheating can make this occur faster, but otherwise, someone could get YLOD after using the system for 2-3 years like I did when my ps3 got the YLOD in 2010 and I had it since 07
others get YLOD within a few months of having their system
neither one could overheat, it could be just the thermal paste is too thin