The marriage between James Henderson and Mary Anne M’Laughlin was registered in the civil records in Londonderry, 1876 Volume 7, page 193. If you order a copy of that certificate, either from GRONI in Belfast or GRO Roscommon, you will find out exactly where the marriage took place and who officiated.
James Henderson’s death in 1884 is registered in Inishowen Apr – Jun 1884, volume 2, page 99, with the age recorded as 70 on familysearch. Again, if you order a copy of that certificate you will be able to judge for yourself whether there is any confusion over the age. (Which was simply the informant’s best guess).