They are prone to parasitic infection until they reach sexual maturity...
White stringy poo is a sign of internal parasites...
I use UV lights to prevent parasites... If signs of infection are seen, treating as directed with a parasite product sooner rather than later will help... I've heard good things about Jungle Parasite Clear, but have no experience with this or any other parasite products.
They grow fairly slow when they are tiny babies... they are unlikely to keep up with the fastest growing standard Dempseys, but don't necessarily grow real slow...
I cannot comment on their overall lifespan, but I know of no reasons why they shouldn't live as long as a typical Dempsey. My oldest one is a bit under 4 years old, is 9" long, very beefy, actively breeds and can compete with other Cichlids just like I would expect a standard Dempsey of his age/size to...