The manifest for Lord William Bentinck in 1841 says "John 35 Agricultural Labourer", which would make him born around 1806. Maybe this is him...
John Francis. born 23 Mar 1805, baptised 14 Apr 1805, Maidstone, Kent.
father John, mother Philadelphia.
John Francis m Philadelphia Osborne. 22 Apr 1804, All Saints, Maidstone, Kent.