My DS has "built up" teeth as he broke both his permanent fron teeth at about aged 8.
To strat with I believed they would give him veneers once his orthodontic work had finished, as no point capping/crowning/veneering a wonky tooth, but now his braces are off the dentist & Orthodontist recommend we leave any permanent work until he is an adult.
They are very happy to keep replacing the "filling" bits as they do discolour & break, but to have anythhing else means reducing what is left of the tooth for the veneer/cap to fit, and as they are young (and boys) liable to v.expensive breakages. They will not last forever, and for every replacement more of the original tooth will be lost, so delay as long as possible.
Of course, we had broken not discoloured teeth, but they may advise whitening?
Hope you get something sorted before he gets too self conscious. My DS couldn't wait for braces to fix his teeth, as he has had problems since knocking a tooth out aged 3, but now looks lovely