New to cycling, questions about over doing it
It depends on a lot of things, like how fit you are to start with and how well the bike fits you. The same distance can be a very different amount of effort depending on the surface, incline etc. But as a general rule (and assuming you're in decent health) tired is fine, muscle aches are to be expected, but don't ignore pain especially in your joints. As with any new exercise, do build in some rest days, and expect to build up what you can do.