On wedding invitations, etiquette authorities agree, the year is traditionally written as text. It is for this reason, I suppose, that some authorities think to address capitalization of the year. However, there is no consensus. It is more common to see the advice to capitalize the first word of the year (only). Most Google search results for [ capitalize year wedding etiquette ] give this advice.
Mesa County, Colorado (CO) County population in 2014: 148,255 (87% urban, 13% rural); it was 116,255 in 2000. County owner-occupied with a mortgage or a loan houses and condos in 2010: 29,788. County owner-occupied free and clear houses and condos in 2010: 11,718. County owner-occupied houses and condos in 2000: 33,306.
People in group quarters in Mesa County, Colorado in 2010: 1,353 people in college/university student housing; 663 people in nursing facilities/skilled-nursing facilities; 447 people in local jails and other municipal confinement facilities; 331 people in workers' group living quarters and job corps centers; 298 people in other noninstitutional facilities