John Luke and Mary Kate Robertson say faith, not age, is key to a lasting marriage

John Luke and Mary Kate Robertson feel confident that their marriage will last a lifetime because they have God in the centre of their relationship.(Instagram/Mary Kate Robertson)

"Duck Dynasty" star John Luke Robertson, 19, recently tied the knot with his girlfriend Mary Kate McEachan, also 19, in the Robertson's family farm in Louisiana. Amid their wedded bliss, the two have received some criticism for marrying at such a young age.

John Luke and Mary Kate have responded to this criticism, saying that they believe the secret to a happy married life should not be based on the couple's age or the number of years they've spent together, but rather the time they've spent together centred on God.

"As far as relationships and marriage goes, we've discovered that the ones that put God first in their relationship last and the ones who put themselves first don't," John Luke told the Richmond Times.

"Our relationship is based on God in the fact that through His word, marriage is something holy and sacred, so we're in this to make that holy and sacred marriage," he added. "We know we're going to stick together and figure it out no matter our emotions."

His parents, Willie and Korie, also married at a young age, John Luke said. And the newlyweds look up to his parents, who have spent over two decades happily married to each another, as his basis of an ideal marriage.

"I know my parents married young as well, and they have always been examples of what 'could be' to me," he earlier said. "Fast-forward 22 years and they are more in love than ever, and I hope Mary Kate and I are the same way in the years to come. God has truly blessed us."

The two are now attending college in Liberty University, which is the largest evangelical university in the world. It is located in Lynchburg, Virginia, which is several hours away from home. Mary Kate has admitted that they feel homesick sometimes, but being together to navigate through college has been a big help.

"I don't know if college is going to add stress to our marriage or not," mulled Mary Kate. "But that might make our marriage even stronger because with us both being under stress, we'll come to each other and cling to each other."