For @54 years, you have had your permanent "adult" teeth and you still have them! Congratulations, they have worked night & day, 24h non stop for over a half of a century. In that time, organic stains and possible thinning of the enamel from attrition and/or acids in diet could make the interior of the tooth more visible. That interior is also more porous and stain grabbing.I have had great results utilizing "Deep Bleaching" techniques, basically using two whitening methodologies as one larger bleaching session. If that doesn't whiten, I usually will credit the cost towards ceramic veneers or crowns if physical coverage of the teeth becomes the only patient acceptable way of reaching their cosmetic goal.White teeth are still attainable, good luck!