Of or involving the cells of an organization or movement: The assessment of opposition to any totalitarian regime ... is notoriously difficult, for any effective movement must be secretive and cellular (Anthony Sampson). 4. Of or relating to a cellular telephone.
In the past, a human generation has been considered to be 20-25 years. Older genealogical documents will use these numbers. However, genealogical studies have revealed that this is too simplistic and can result in large inaccuracies during statistical calculation.
Quite a difference when counting over hundreds or thousands of years. Today, in our secular world, a generation may be as short as 18 years like the 'baby boomers' (1946-1964) and as long as the frequent 100 years - the most common time is 40 years. Final thought, the term  generation  may have other meanings too.