Timing Belt

Unless you are having problems, and I don't think that you are, I would change it. If you have to take it to a mechanic, it will cost you $$.

if it is an interference motor you should take the advice more seriously but I think 31K is a low # to worry about it ,

The belt is old so I would change it.

F_O_R is right again , The belts 14 years old

Change it. 14 year old timing belts are just waiting to bend the valves.

Yup...change it based on age. But to remove the mystery of condition just remove the left front plastic cover's 10mm bolt, pry the cover back an inch, and peer in there to check for cracks in several locations (jerk the starter to adjust rotation). You can push the belt's top run down with your finger to check the tensioner too! Will take less than 5 minutes. Only if the belt is PERFECT would I drive it. Most of these belts crack after 10-12 years. Figure 3 hours labor to replace the belt, checking the tensioner for oil leak (that's how they fail) and the idler for play anyway. You can safely OMIT the water pump as they never fail. So maybe you can keep this under $400 if only the belt is needed. Good luck. And yes: the odds of bending a valve and tossing the whole car are great if the belt breaks while running.

Cheap insurance which allow your car to run for a very long time given the low miles.

I would also ask an experienced Subaru wrench to check the head gaskets for seepage. Since the t-belt replacement is included in a $1.5k-ish HG job, you do NOT want to replace the t-belt and have to eat that $400 if HG leakage is significant. Look especially for a COOLANT leak at the left rear lower corner (cyl #4), as well OIL leakage from the RIGHT head side. The former will be evident as greasy green wetness across the left side rear underbody near the trans, whereas the oil leakage will be predominant onto the catalytic converter on the right side...usually creating a smelly mess. If you need HGs ensure that an experienced wrench does the job, and that the heads are sent out for careful inspection at a machine shop (this will be a sublet of about $150). If either head is "running a wet diaper", but not yet bleeding onto the ground nor cat conv, do NOT replace the t-belt IF it looks un-cracked upon inspection. Even if we're wrong, and it snaps, a used motor is $1.5k and $500 to install...not much more than a $1.5k HG job. Capice?