Why is the percentage of elderly people usually smaller in LEDCs than in MEDCs

In a LEDC an older person usually has no pension for income so they are made to work to an extremly old age, possibly they have lost their younger familly members that supported them before. In an LEDC there is no proper health service, disease spread easily in the slums and sheds they live in. The Climate in an LEDC could be hotter e.g Africa and clean water and proper sanitation could be hard to find thus making it difficult to work and live. Tecnology is scarce, proper tools for independent food gardening are not availiable and they might starve. MANY factors can affect the population pryamid of an LEDC, just think of it logically.