It is an interesting concept however it does appear to have some easily named exceptions as others have pointed out. It also though has a lot of overlap with reproduction selectivity (r/K theory). Namely animals with shorter lifespans breed quicker and have more offspring than animals that live longer and have longer gestation periods.
Think about it... you have an elephant which takes nearly 2 years to come to term, it would make no sense to have a 10 year life cycle. Instead, they can live 60-70 years. Think dogs and cats. Cats have anywhere from 2-4 kittens on average; dogs 6-10 puppies. Cats can live easily 20-30 years, dogs 10-20. Which one is bigger? Then again, wolves tend to have smaller litters and breed less often than dogs so maybe we tinkered with that.
So I guess my point is he has stumbled upon something (which may already be known according to other posters) but that it heavily overlaps with other theories. Now maybe size does play into r/K theory. From a high level view you have things like elephants, whales, humans and other large mammals that breed rarely and live long. Also I suppose its difficult to compare mammal verse reptile here. A tortoise lives a long time and lays many eggs but thats kind of how reptiles work. I don't know that it is a valid exception since it has reasons for not investing in raising children and to take a shot gun approach to it.