2005 altima,4 cylinder. 170,000 miles. 65 to 70 mph with a/c getting low 20,s mpg . same for everyone ?

2005 altima,4 cylinder. 170,000 miles. 65 to 70 mph with a/c getting low 20,s mpg . same for everyone ?

You should be getting in the high 20s, maybe 30 mpg at those speeds. Mileage is high, so there could be a number of maintenance issues that are causing low mpg. Here are some things to check:
1) recent oil change (I would recommend lowest possible viscosity, check your owner's manual; use full synthetic)
2) most recent tune up (spark plug and wire change [new plugs and wires are typically recommended every 100k miles]; check distributor cap; check engine timing; check O2 sensor; check PCV; clean injectors and throttle body; new air filter; new fuel filter)
3) check compression - too high of compression indicates excess carbon deposits in your cylinders; there are a couple de-carb techniques that would take care of this
4) Tire pressure - fill to max PSI, as rated on your tire sidewall

This should be enough to get you started. Cheers!