No.  Certainly not.  Luther did teach the perpetual virginity of Mary earlier in his career, when he was reflecting his Roman Catholic heritage.  Earlier in his career he had a very high view of Mary, but later he renounced the practice of praying through Mary and the teaching of the Assumption of Mary.  I speculate (and this is just my speculation, so take it with a grain of salt) that if you asked Luther later in his career, it is possible he may have renounced this Catholic teaching of the perpetual virginity of Mary for the simple reason that it is proved wrong by the Scriptures.  It is worth noting that after leaving his monastic order Luther married and had children of his own.   However, there is no writing by Luther in which he renounced this teaching, so my claim is speculation.

Jesus had at least four brothers and more than one sister.  This is proved by Matthew 13:55-56 and Mark 6:3.  Jesus’ brothers included Jude, Joseph, James and Simon.  He had at least two sisters, as mentioned in this passage.  To make Jesus’ siblings into cousins is to set up an ad hoc hypothesis (ie it is not the result of evidence, but an attempt to explain away inconvenient evidence), with no basis in Scripture.

The Roman Catholic Church then and now semi-deify Mary.  They considered celibacy to impart a greater holiness to those who choose this path, and in so doing, they dishonor marriage.  For this reason, they invented the false idea that Mary never had intimate relations with her husband Joseph.   It is quite obvious that the Catholic Church read their false idea about Mary into the Scripture.  They claim that the brothers and sisters of Jesus mentioned in Matthew and Mark are actually his cousins.  This flies in the face of many clear biblical statements, as well as the statements of the very early church fathers.  There is nothing sinful about married people having sex!  There is nothing sinful about Joseph and Mary having intimate relationships, which they clearly did.  This early belief of Luther is rather obviously wrong, and, like I said, I feel it is possible that the later Martin Luther would have rejected his former belief.