Ideally, a fresh developer should equal a seasoned developer. This is why in color you add a "starter" to make this outcome take place. In B&W, the seasoning effect is much less pronounced and the build up in halides in the developer have far less impact on the resulting image.
Generally though, Iodide salts and Bromide salts are restrainers and also can repress edge effects. Included in this list are PMT (Phenyl Mercapto Tetrazole) and BTAZ (Benzotriazole). There are many many more. The initial effect is lower fog, then lower speed and contrast.