In this article I will establish that the age for marriage, when someone is allowed to get married Biblically, is when one enters puberty. The Bible makes mention the general age of girl allowed for “love-making”. The reference is found in a parable where God compares Israel to a baby girl whom YHWH took in and then married her off, later.
Ezekiel 16:4 NIV Translation
4 On the day you were born your cord was not cut, nor were you washed with water to make you clean, nor were you rubbed with salt or wrapped in cloths. 5 No one looked on you with pity or had compassion enough to do any of these things for you. Rather, you were thrown out into the open field, for on the day you were born you were despised. 6 “‘Then I passed by and saw you kicking about in your blood, and as you lay there in your blood I said to you, “Live!”[a] 7 I made you grow like a plant of the field. You grew and developed and entered puberty. Your breasts had formed and your hair had grown, yet you were stark naked. 8 “‘Later I passed by, and when I looked at you and saw that you were old enough for love, I spread the corner of my garment over you and covered your naked body… –
As you read the passage, the girl attained the age for lovemaking after her breast had grown and pubic hairs, these are some signs of puberty. As shown, the Bible does not give explicit age for someone to have relations, but what it does give, reading the passage, ‘puberty’ is the minimum age for relations to begin.
One should be aware here, that “puberty” is not clear cut what exactly means historically speaking. Scholars in the past have deduced at times that when a girl grew few hairs she was considered to be hitting “puberty”, even though she may have not menstruated yet.
Bible Translations: Ezekiel 16:7-8
Ezekiel 16:7-8 Complete Jewish Bible (CJB) And you did increase, you developed, you reached puberty, your breasts appeared, and your hair grew long; but you were naked and exposed. 8 “‘Again I passed by you, looked at you and saw that your time had come, the time for love…
Ezekiel 16:7-8 Expanded Bible (EXB) I made you •grow [flourish] like a plant in the field. You grew up and •became tall [or matured; developed] and •became like a beautiful jewel [or entered puberty; reached womanhood]. Your breasts formed, and your hair grew, but you were naked and •without clothes [bare; exposed]. “‘Later when I passed by you and looked at you, •I saw that [behold] you were old enough for love…
Ezekiel 16:7-8 New International Version – UK (NIVUK) You grew and developed and entered puberty. Your breasts had formed and your hair had grown, yet you were stark naked. 8 ‘“Later I passed by, and when I looked at you and saw that you were old enough for love…
Bible Commentary on Ezekiel 16:7-8
John Gill’s Exposition of the Whole Bible
Verse 7 …thy breasts are fashioned; swelled and stood out; were come to a proper size and shape, as in persons grown and marriageable; see Song of Solomon 8:10;
and thine hair is grown; an euphemism, expressive of puberty, which in females was at twelve years of age… 
Ezekiel: A Commentary – Dr Paul M. Joyce,
‘You were thrown out in the open field’: the exposure of babies was commonplace in the ancient world. 16:6. “As you lay in your blood, I said to you, ‘live!’”:…The Hebrew word rebaba netattik means ‘I made you a myriad (that is, ten thousand),’ in other words ‘I caused you to flourish’; this does not require emendation. ‘Full womanhood’: the Hebrew cadi cadayim means literally ‘ornament or ornaments.’ …….16:8. ‘you were at the age for love’: puberty; the emphasis here is more on sex than affection… ‘I spread the edge of my cloak over you’: Kruger (1984) explores the meaning of the symbolic gesture here and in Ruth 3:9, not merely an act of charity but a declaration of a new relationship. ‘Entered into a covenant’: a double sense, referring both to marriage and to a theological covenant…. 
Abingdon Old Testament Commentaries Ezekiel – Nancy R. Bowen
…The baby girl arrived ‘at full womanhood,’ that is, sexual maturity, as her ‘breasts developed’ and her ‘(pubic) hair had sprouted’ (author’s translation). She was ‘ripe’ for marriage. Between birth and puberty there is no mention of further divine care… 
The Jewish Study Bible: Jewish Publication Society Tanakh Translation,
6-7: God wills the abandoned infant to live. She lives and grows to puberty. ‘Live in spite of your blood’, may also be understood as ‘live because of your blood,’ and with this understanding these words are incorporated in the circumcision ceremony. 8: Upon reaching puberty, she is ready for marriage... 
In addition to the above Bible commentaries, here are more scholarly discussion on the passage. Marriage as a Covenant: Biblical Law and Ethics as Developed from Malachi – Gordon P. Hugenberger,
Although the Old Testament nowhere explicitly states the typical ages for marriage, the mention of the ‘age for (sexual) love’ in Ezek. 16:8 may suggest that women generally married soon after puberty. 
The Song of Songs: A Continental Commentary – Othmar Keel,
[8:8] Ezek. 16.7 names the development of the breasts and the growth of pubic hair as signs of puberty (when the girl became eligible for marriage). 
Berit Olam Studies: In Hebrew Narrative & Poetry The Song of Songs, – Dianne Bergant & David W. Cotter,
Developed breasts and appearance of pubic hair were signs of puberty and signalled the woman’s physical preparedness for marriage (see Ezek 16.7). 
I briefly need to mention again here, when some of the commentaries say, ”puberty”, this is very ambiguous. According to classical Rabbis and contemporary scholars “puberty” here, this does not equate to that a girl has menstruated, but rather a girl could be called by that term for only having two pubic hairs (or armpit).
In conclusion, the Bible provides no explicit age for when a girl is allowed to get married. But, what it does give us is that YHWH – God of the Bible, allows for marriage to be consummated when a female has hit puberty (i.e., grew few hairs). 
Age of consent in America & Europe – historically
12 year old Mary’s marriage to Joseph the Carpenter
Bible on pre-pubescent-marriages
Isaac’s Marriage to Rebecca
 John Gill’s Exposition of the Whole Bible, Ezekiel 16:7-8 http://www.studylight.org/commentaries/geb/view.cgi?bk=eze&ch=16#1
 Ezekiel: A Commentary [Copyright 2007, 2009] by Paul M. Joyce page 131
 Abingdon Old Testament Commentaries Ezekiel [Copyright 2010], by Nancy R. Bowen page 85
 The Jewish Study Bible: Jewish Publication Society Tanakh Translation [Copyright 2004], by Adele Berlin, Marc Zvi Brettler, Michael A. Fishbane page 1068
 Marriage as a Covenant: Biblical Law and Ethics as Developed from Malachi by Gordon P. Hugenberger page 315
 The Song of Songs: A Continental Commentary [Copyright 1986], by Othmar Keel page 278
 Berit Olam Studies: In Hebrew Narrative & Poetry The Song of Songs [Copyright 2001], by Dianne Bergant and David W. Cotter, page 100
 Evangelist Pastor Tony Alamo:
“During a 2008 interview with CNN anchor Rick Sanchez, Alamo ranted against the Catholic Church and argued that the Bible implies that puberty is the age of consent.
“I don’t know when girls reach puberty. Most of them around 10, 11, 12, 13, 14,” he said during the interview. “God inseminated Mary at the age of around 10 to 12. Should we get him for having sex?” (“Women: We were child brides in U.S.” (23rd June 2010), http://edition.cnn.com/2010/LIVING/06/23/o.child.brides.stories/index.html )