The birth date is most likely an estimation. Estimations are quite common in files.
However, he has 2 mothers listed. Either 2 different people were merged together or the wrong mother is listed as main.
12/26/2009 at 6:29 AM
I have this profile in my tree (pending merge now into the profile Denise linked to) and I have two profiles (that also need merging) for his mother Dorothy Griswold (James).
One profile has a death date of 1615 and the other at 1630.
Thomas was born after Mathew in 1622, which would have put Dorothy at the age of 55. So I'd say this relationship is suspect, perhaps some of these children were actually grandchildren living with her. I don't know this family and have never researched it.. just making guesses.