it's not measured in years but in units of thrash which are crank revolutions x pedal force applied. typical Al frame can only take a small amount of thrashing compared to other 'noble' material which can handle huge thrashing loads. there are tales of some well crafted steel frames surviving a severe beating (10E0 thrash).

After 25000km (2 years) my Al training bike frame is getting floppy around the BB. Replacement cost? ~$400. That's cheap considering it costs me over $300 every 3 months to replace the chainset and another $120-150 in tyres and tubes.