The word generation derives from the word Genesis.

A generation is  group of individuals, most of whom are the same approximate age, who were born in the same period of time, having similar ideas, problems, attitudes, etc.
A generation is time frame when something that started from a point of time, generates into the state of it’s full maturity.

(Generation of war, generation of industrial development, generation of economical prosperity, generation of Internet etc).
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a group of individuals belonging to a specific category at the same time:
Chaplin belonged to the generation of silent-screen stars.

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a form, type, class, etc., of objects existing at the same time and having many similarities or developed from a common model or ancestor (often used in combination): a new generation of anticancer drugs;

Generation is the psychological status (way of doing things, mindset, natural environmental energies) which are dominating or ruling in a given period in time.

(He was born in a time when people were selfish)

Human’s or organism’s biological clock can be very much influenced by the season in which a person was born.

For example; if a child is born in a time when certain psychological developments or changes were taking place, (like the generation of the Internet, generation of free thinking), then biologically the biological clock of that child will automatically adjust it’s self according to the seasonal time in which the child is born.

Then the child’s natural ability (of intelect, talents, desires) will reflect the generation in which the child was born.