In our experience, beagles typically mature and 'calm down' at about 2 years of age. By that I mean that they are housebroken and can be trusted in the house on their own when we are home.
We always, however restrict their access to the house when we are not home. We either crate them or contain them in our kitchen with baby gates limiting their access to just the kitchen area.
Occasional 'accidents' of the housebreaking kind might happen, but they are few and far between.
While the pups are young, they are not allowed unlimited access to the home without strict supervision, and we have always maintained a strict crate training routine. We have housebroken two puppies that we have raised in this way, and we have had much success. The pups earn 'privileges' (full access to the house, etc.) with supervision after about 6 months of age and continue to mature until they understand the 'house rules' at about 2 years of age.
Others' experiences may vary, but this has been ours.