If you take care of it, your iPod Touch could last you 10+ years. The battery is a different story.
The answer is: it depends. If you're charging from 0% to full every day, it won't last as long as if you charged from 75% to full.
I believe the current iPod Touch battery is rated for 1000 charge cycles, so assuming you charged from 0% to full on a daily basis you could reasonably expect to get ~1000 days, or a little less than 3 years, out of it before needing a battery replacement.