The short answer is: a long time with proper care. You can read up on lifespan, etc., at this site: http://www.sulcata-station.org/faq.html#lifespan. That site also has other references you may find interesting about sulcata care and history.
Yes that's what it says that is why I gave you the link so you would know they couldn't find any specific information about sulcata lifespan so they likened it to the Galapagos. I'm afraid that's as good as the information gets....over 100 years is not out of line with a large tortoise. I'm sorry the info wasn't more helpful to you.
What about lifespan for smaller torts like my Taco? Is there a lot of variation among species or is it consistent? One source I read said 50-100 years. Does this sound right?
That sounds right, Stephanie, however, Taco's life might be shortened because of his pyramiding. His bones are also affected. But just give him the best you got and hopefully he'll outlive you!
On the Sulcata Station website, if you click on the last Fact Photo on the right it says this, " The oldest known of this species was 56 years old although it is believed they can live up to
about 80 years."