Pope Benedict wrote that there is no tradition of an older man marrying a consecrated young virgin for her protection in Judaism, and so that claim is not effective to explain Mary’s somewhat puzzling statement to the archangel Gabriel.
It’s considered a pious belief but not canonical or scriptural. The celebration originated in the Byzantine Church (as did the apocryphal Evangelium, I think), so it is venerated as an early feast day of the Eastern churches. In the Roman Catholic Church, we celebrate it not as a commemoration of a temple consecration by Mary, but “we celebrate that dedication of herself which Mary made to God from her very childhood under the inspiration of the Holy Spirit who filled her with grace at her Immaculate Conception,” (that last from the Liturgy of the Hours for November 21) while honoring the ancient tradition of our eastern brethren.
Pope Paul VI in the 1974 encyclical Marialis Cultus, n.8, wrote of this feast that “despite its apocryphal content, it presents lofty and exemplary values and carries on the venerable traditions having their origins in the Eastern churches.”