Yes this is a tricky one. William Vondy the Blacksmith married to Elizabeth Kneale in 1800 was born c1767-71 based on the 1841 census info. This would make him c29-33 years old at marriage which is okay.

I thought he was a son of William Vondy and Margery Christian who married in 1765. So he was born about 2-6 years after the marriage which is normal.

IGI have a William Vondy born 30 May 1773 in Lezayre to Wm Vondy and Margery Christian. Problem... this William Vondy is too young to be 70 in 1841...

Mmmm. I'll have to re-think this!