From the life expectancy of individuals. The nature of the age structure is associated with the biological characteristics of the species, the stage of the life cycle, and environmental conditions. The simplest age structure is characteristic of populations of organisms with a single reproduction and short life expectancy. These are annual herbs, for example, Ivan da Maria or medicinal chamomile, which are widespread in central Russia. Thus, populations of these species at any time are represented by individuals of the same generation and age. In organisms with multiple reproduction and a relatively long life span, the age structure is much more complicated. In such populations, individuals of different generations are simultaneously represented. For example, any grass frog population in spring consists of animals of different ages that are asexual and ready to breed. In mid-summer, when metamorphosis ends, the population includes frogs of new and previous generations.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.