adjective

(of a person) firmly established in a particular habit, belief, or way of life and unlikely to change their ways.

a confirmed bachelor

established,long-established,long-standing,firm,committed,dyed-in-the-wool,through and through,seasoned,hardened,settled,set,fixed,rooted,staunch,loyal,faithful,devoted,dedicated,stalwart,steadfast,habitual,compulsive,obsessive,persistent,unapologetic,unashamed,incorrigible,irredeemable,unreformable,impenitent,inveterate,chronic,incurable,deep-dyed,card-carrying