I love the setting - Republican Era. I wish we had more C-dramas set in this era instead of the Dynasties. Costumes and set design are lovely.

Now, the age difference. I honestly don't know how old ML is supposed to be when he rescues FL or how old FL is supposed to be. The actor looks like he's in his 30s, but the screenwriter/director might want him to be in his 20s when they meet. After all, he does not look 40+ after FL is grown up. There looks to be maybe 10 years difference between ML/FL during the majority of the film so I'm going with that. Also, we need to remember the time period in which this takes place. It was common for older men to marry much younger women. It was only recently that society started frowning on such relationships. Also, I'm going to assume that FL is at least 18 years old, but keep in mind that prior to the 1900s, 15 year olds did marry. They had to - disease & war would wiped out young people as well as old. It was only in modern times that both men and women married later in life. Also, childbirth took out a lot of mothers so the younger you were, probably better your chances of survival. It's important to consider the context and history in which a drama is set and not judge the characters by modern standards.

If you can't handle the age difference, then don't watch it, but I would recommend not even paying attention to the beginning. Just concentrate on the 90% of the drama in which the actor/actress looks close enough in age to not be creepy.