What about Switzerland? Modern-day Iranians are the descendants of Persians who date back to Biblical times, and I’m not aware of their country ever being dominated.
Someone mentioned WWII and Japan. I’ve never heard of Japan being conquered/occupied at any other time in history, and the U.S. occupation was both very short and left no major cultural impact. I think Japan and England are probably the closest to the criteria in the OP. Realistically, probably only an island nation qualifies. All others are too easily invaded.
France conquered Switzerland after the French Revolution.
Persia has been conquered a number of times, such as by the Turks and Mongols.
The only time Japan was conquered prior to WW2 that I can think of is the theorized prehistorical migrations from the mainland. While I don’t think the US Occupation (1945-1952) made the Japanese not “Japanese,” or anything, it did have a massive cultural impact on the country.
Perhaps Thailand might be in the running?
The OP sets up conditions that can’t be fulfilled by any of the countries yet suggested. If we ignore the more unreasonable of these conditions, then Britain, Japan and China all are in the running.
Lizard[ to History: I quit!
…and the empire under Chingis, while it encompassed the kingdoms of the Jin/Jurchen and the Tanguts/Xi Xia/Hsi Hsia, all parts of what would today be considered China, it did not include the Southern Song south of the Yangtze river, whcih is generally accepted to have been the only legitimate Han Chinese regime. Since modern day Northern and Western China were already controlled by Non-Han rulers, including the Mongols, the Song kingdom was generally thought of as China “proper”. The Southern Song was conquered under Khublai, who at the time had already in practice split with Hulagu’s Il-Khanate in the Middle East, and the Golden Horde of Eastern Europe ruled by the descendents of Batu. Three generations of Mongol Rulers, Chingis, his son Tolui, and Tolui’s son and Khublai’s brother Mongke, had passed before Khublai finally defeated the Song and conqured China “proper”. It was under Khublai that the Mongol empire in the east switched from being called the Great Khanate to the sinicized Yuan dynasty.
So, most people generally accept that it was Khublai, and not Chingis, who was the final conqueror of China. 
Naturally, I counted Ogodei and Tolui to be of the same generation. 