] George was born in 1731 and Cassandra in 1739, so about 8 years difference in ages.

So if George and Cassandra had eight children: James (1765), George (1766), Edward (1767), Henry (1771), Cassandra (1773), Francis (1774), Jane (1775) and Charles (1779), then Mother Cassandra gave birth to Jane at age 36 and Charles at age 40. Seems bold to give birth at such an advanced age in those days, especially since mothers seemed to die in childbirth quite often.