The meaning of the word 'sinewy', in this context, is <em>strong, muscular</em>.
In Emily Bronte's <em>Wuthering Heights</em>, Joseph is an elderly servant. He has been working at Wuthering Heights and serving its residents for decades.
In this excerpt, Bronte implies that although he was old, Joseph was <em>"hale and sinewy."</em> Word hale means <em>"strong and healthy"</em>, while the adjective sinewy indicates that he was fit for his age.
