I found these burials.
bur. 4 Mar 1835, St Nicholas, Harpenden, William Munt, aged 58 [1776/7]
bur. 2 Aug 1846, St Helen, Wheathampstead, William Munt, aged 82 [1763/4]
bur. 29 Jan 1823, St Nicholas, Harpenden, Sarah Munt, aged 40 [1782/3]
which may at least give some pointers on approximate date of birth.
R