It is interesting that nowhere in the New Testament is there any mention of the 1st century believers celebrating the birth of Jesus and yet all the disciples continued the traditional Jewish feasts.
Yes it is. In fact Paul instructed gentiles to keep the feasts of the Lord:
1Co_5:8 Therefore let us keep the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.
Paul was referring to the days of unleavened bread. And the greek is clear that the Paul is talking about celebrating the feast of the Lord.