There is no way to tell if a 5 year old helmet is safer than a 6 or 7 year old one.Any brand of helmet may just barely meet Snell stands or is off the chart for safety. Snell doesn’t report that. More expensive helmets made today may exceed future standards.

If the bike was in decent shape when put away, and has not been exposed to the weather, there's probably very little that needs to be done. The tires would be the biggie -- likely they're checked and may need replacement (though not for certain). Inflate them to listed pressure and check the sidewalls for cracks or bulges

One of the most basic biking rules is this: When you are riding your bike, you need to act like you’re driving a car. And when you are walking your bike, you need to act like a pedestrian. That means you ride your bike in the same direction as the traffic (not against it).