You can leave your sourdough starter on the counter at room temperature as long as you continue to feed the sourdough starter.
The sourdough starter can either be kept at room temperature or in the fridge.
A sourdough starter that is stored in the fridge will only require feeding once a week to maintain it.
If you use your sourdough starter every day, keep it at room temperature.
Follow the feeding instructions and then leave it at room temperature.
Every morning or every night, discard half of your starter.
Feed it and let it sit while it eats the flour.
Bake with it when it has doubled in size.
As always, how long this takes will depend on the vigor of your starter and the warmth of your room.
Sourdough starter does improve with age overtime and the longer you keep the sourdough starter the better the flavor gets.
However after about 10 years the sourdough doesn't get much better with age and there won't be much of a difference between 50 or 100 year old sourdough starter and the 10 year old starter.
Sourdough starter can be kept for many years without going bad and if you keep the sourdough starter for up to 10 years then the flavor improves.
But after the 10 years there's not much improvement in the flavor or much improvement in the sourdough starter itself.
But you can use very old sourdough starter and still get great results.
Most people use the sourdough starter well before 10 years but I've heard of some people keeping it for over 50 years.