Utter catastrophic failure after 2 years....
No not really..jkjk. I guess you really can't put a time line on any laptop b/c each one will depend on specific variables like how well you son treats and maintains the computer. Also it depends on how well built is that specific model you buy.
It would be better to ask "how well is the quality" of _________ laptop, so you can guage the longevity of the machine. It would be better to go online and read extensive reviews of each laptop model from customers and pros.