You can drink well water safely and the majority of well water from wells is safe to drink without any filtering or treatment.
Some wells may be contaminated if not maintained properly but disinfecting the water well with some bleach and then flushing the bleach out can make the well water safe to drink.
It's always good to have the well water tested before drinking but many people do drink well water including myself and with a good quality well the water in a well is some of the best tasting and healthiest water you can drink.
Even if the well water smells like rotten eggs which is Sulfur the well water is safe to drink.
Water in a deep well can be as old as 1,000 years to 1 million years or even older.
Water wells are usually drilled deep into the rock and can go from 50 feet to 100 feet and even deeper.
Some water wells are as deep as 200 feet to 300 feet or more and some water wells can be as deep as 800 feet to 1000 feet depending on the depth of the groundwater in your area.
My water well here in Arkansas is 100 feet deep and is drilled through rock and water here is plentiful and so plentiful that sometimes water comes up out of the well when it overflows due to so much rain.
I also have another well that is not in use right now and I use it to monitor the depth of the water and sometimes it even overflows as well when we get a lot of rain.
Deep well water is water that has been in the well for several years and has been filtered through the earth and is safe to drink as long as there is not bacteria in the well.
Well water is usually much safer to drink than surface water and is healthier and safer to drink that city water that is disinfected with chlorine and other chemicals.
The water that has been flowing through the ground could've been there for millions of years but even when you extract the water it eventually goes back into the earth and when it rains again the rain seeps into the ground and eventually recharges the groundwater aquifer.
Wells in drier locations may run dry during drought or run dry when too much water is extracted but wells in places where they get a lot of rain such as in Arkansas are unlikely to go dry but it can still be possible.
Even then a well can recharge and even drilled deeper if needed.