The early church was made up of Jews --Jews by birth and Jews by conversion. Later Gentiles came in and there was a conference in Jerusalem to decide how much of the Old Covenant law a Gentile would be expected to keep. This is recorded in
Acts 15 and happened in the AD 49/50 time period.
Those who came in from a Jewish background kept many of the customs such as sabbath keeping, food laws, and even the Nazirite vow. The Apostle Paul evidently kept the Nazirite vow at times, allowing his hair to grow long (leaving it uncut) for a while then shaving it off and offering the appropriate sacrifice. Apparently he felt OK offering animal sacrifices and keeping some of the old laws because he did not consider them salvational and therefore observing them did not violate what he wrote in Galatians.
And, it seems that keeping the Nazirite vow did not violate what he had written in 1 Corinthians about veils and hair length. Hair length was not an issue in the Old Testament. Both men and women could make a vow and not do the normal hair cutting but let their hair grow for a specific period (even for life) and then shave it off. The passage in 1 Corinthians is difficult to understand and seems to reflect Paul's recommendation to not flaunt liberty if it offended local moral customs.