Celts captured Rome except for the Capitoline hill in 387 B.C. and occupied the Po Valley in Italy for centuries. In the 3rd century B.C. some of them invaded Greece. Eventually they settled down in Galatia in Asia Minor. St. Paul traveled through there (Acts 16.6; 18.23) and wrote a letter to the Galatians--but the letter is in Greek and there is nothing to show whether the recipients were of Celtic ancestry. (They could be descended from Greeks who had settled in that area, or of other non-Celts in the Roman province of Galatia who had become Greek-speakers.)
Probably there were many similarities between the customs of the Thracians and the ancient Celts. Herodotus said that among the Thracians "to live by war and plunder is of all things most glorious."
Yes, there were many similarities, and you are correct, no time was indicated.
My offhand comment was with regard to "The Thracian tribes were ruled by a powerful warrior aristocracy rich in gold treasures." Of course there were other warrior led tribes, and lots of people liked gold treasure, but one of the things that follows the Celts all the way from their origins in NE asia throughout Europe is their love of gold and their unique artistic ability to work in the medium. Museums all across Europe are full of stunning Celtic gold art.
Eventually they settled down in Galatia in Asia Minor. They didn't "settle down" and just disappear. They continued to grow and became the dominant peoples of western Europe today. (Regrettably, even the French are Celtic.) How long they remain dominant remains to be seen, with the most popular newborn Male name in Belgium now "Mohammed".
That almost sounds like Vikings, doesn't it?