What kit used, waterpump too ?
6 years is not that high, UK subaru do 6yr, US do 8yr. OEM belts staying under the service mileage would do 8yrs quite easily I expect, well a lot do actually from what I see in :-)
If you doing quite high miles a Dayco belt & quality waterpump (don't buy cheap pumps) could be worth the investment & piece of mind.
Up to you & your budget at end of day.