Are there any generally accepted rules or formulas as to which is more important to resale - age or miles? Let’s say it’s a car with a good rep for low maintenance like a Toyota or Honda.
Of course there are - the people at Kelley Blue Book and NADA have them. 
On an aging car, both are important, and the car’s maintenance history will play a part as well. All of the rubber stuff - tires, hoses, belts, etc. will deteriorate both from use (mileage) and from simple passage of time.
If you want to know what people will pay, then all theories are out the window, and you can check KBB or NADA as gotpasswords suggests, or - even better - look at a site like GetAuto.com for your area.
As for what’s actually a better idea for you to buy, obviously it will depend on how many miles versus how many years of age. But there are two arguments in favor of newer high-mileage cars over older low-mileage. 1) Newer high-mileage cars will tend to have accumulated those miles son highway commutes, while older low-mileage cars will tend to have been driven more stop-and-go local driving. 2) Even assuming the amount of wear-and-tear on the two cars is equal, the fact is that cars have been improving over the years, so with the newer car you’re getting something that started off a better car. (With exceptions, of course.)
Whether or not the previous owner did the routine maintenance on time is very important, and undercarriage rust is important.
A mechanic can tell you these things by looking at the car and doing things like compression tests. It’s imperative to check the compression on a car, even a newer one, with high mileage, and to make sure the timing belt was changed on time. On an older car with low mileage, it’s important to inspect for rust, and if it’s a big car, signs that it has been used to haul things (like a boat). If half the low miles were under a load, then it’s not such a bargain, mileage-wise.
Also, if is has* really* low mileage, then it may have sat during half of every year, if the owner traveled, or something. Find out how the owner stored it, and if it sat with a lot of gas rotting in the tank.
PS: with high mileage on a new car, you get the up-to-date safety features and the other up-to-date things, like the bluetooth sound system, and on-star.
I have never seen any evidence gas rots in the fuel tank. Maybe after many years.
Less time than you would think; say a couple months. Ask anyone who owns a motorcycle or plays around with old bikes that haven’t been ridden for a while. If you park it with say half a tank you will get a little bit of a “red beard” above the gas level just over the winter and one can seriously start to roach after a couple years. Its one of the reasons we usually suggest topping it off if your going to have it parked half the year. Also newer gas breaks down and the ethanol part can cause issues unless you drain and refill the tank or use a stabilizer during your last couple fill-ups.
Good advice, and I’d like to add an additional step. If you’re buying from an owner, take a good look at his house/apartment if possible. IME, the general condition of the house, yard, other cars, etc. is a reliable indicator of his maintenance habits.
Some cars seem to be designed with a certain amount of miles before things start to fail. I’ve owned a series of BMW’s and they have a host of things that end up breaking around the 100-120k mile mark. I almost more willing to buy a BMW with 120K+ miles where I know the owner replaced all that stuff than buy one with 90K since I know I’ll end up having to fix it. Age is important, but the closer it is to that failure period the more influence the age will have on my decision.