Forbidden? In New Testament times, long hair was considered disgraceful by jewish men as well as those in 1st century Corinth. The portraits rendering Christ with long hair are based in Middle age imagination, not biblical accounts. A fact that can be seen in thousands of paintings ans sculptures of the day.
There is something called the Nazarite Vow, where a man did not ever cut his hair, or eat grapes- or take wine. This had to do with his covenant with God. Samson, John the Baptist, took that vow.
In the New Testament, the Bible speaks of the covering of a woman's head in prayer; saying that a woman should have long hair, which is a glory to her. It says also that nature teaches that if a man has long hair, it is a shame to him.
Verses 13-15
Judge in yourselves, is it comely for a woman that a woman pray unto God uncovered.? Does not even nature itself teach that if a man have long hair it is a shame to him,? But, if a woman have long hair, it is a glory to her; for her hair is given for a covering.
Reading the entire chapter makes it clear that the head you shame by having the long hair as a man- or having short hair, as a woman; is the head of the Body of Christ; which is Christ, Himself- verse 4
This does not conflict with biblical history, but with the artists