The Hebrew word translated "son" can also have the meaning of "grandson," "great grandson," "descendant," etc.
An accurate understanding of biblical genealogies is difficult, yet it is important for the understanding of Scripture.
As indicated earlier, the Bible does not fix the age of the earth, contrary to the claims of Answers in Genesis.
There are a number of other assumptions implicit in the calculation.
The first, and foremost, assumption is that the genealogies of Genesis are complete, from father to son throughout the entire course of human existence.
Instead of creating a world filled with full-grown plants, God actually created seeds and planted those.
We understand this from the word "sprout," which refers to God allowing the earth to produce plants through germination (sprouting).