I completely disagree! it is never too late... until it is too late and nothing can be done, but in so MANY cases it is simply not true! and experienced with frogs vet can help with that.
Ellis - a lot of things can go wrong like with any being, MBD is the most common one in young fast growing individuals, there is no age/size to start having problems, anything can happen at any given time, some conditions will be obvious early , some later in life. That is why the owner have to provide proper conditions and nutrition, and constantly keep an eye on anything out of ordinary so he can react accordingly in a timely matter.