On one hand marriage is seen as a way to contain sexual love and on the other the Church is holding back on allowing people to marry as soon as possible so that they can contain that love in the bonds of matrimony.
Sex inside of marriage is not legal fornication. Mariage isn't for containing sexual intimacy, the sexual intimacy is a means of sharing and expressing the bond of marriage (in order to properly express the bond of marriage, that marriage must exist).
1 Corinthians 7 (King James Version)
1 Corinthians 7
1Now concerning the things whereof ye wrote unto me: It is good for a man not to touch a woman. 2Nevertheless, to avoid fornication, let every man have his own wife, and let every woman have her own husband.
3Let the husband render unto the wife due benevolence: and likewise also the wife unto the husband.
4The wife hath not power of her own body, but the husband: and likewise also the husband hath not power of his own body, but the wife.
5Defraud ye not one the other, except it be with consent for a time, that ye may give yourselves to fasting and prayer; and come together again, that Satan tempt you not for your incontinency.
6But I speak this by permission, and not of commandment.
7For I would that all men were even as I myself. But every man hath his proper gift of God, one after this manner, and another after that. 8I say therefore to the unmarried and widows, it is good for them if they abide even as I.
9But if they cannot contain, let them marry: for it is better to marry than to burn.
10And unto the married I command, yet not I, but the Lord, Let not the wife depart from her husband:
11But and if she depart, let her remain unmarried or be reconciled to her husband: and let not the husband put away his wife.
12But to the rest speak I, not the Lord: If any brother hath a wife that believeth not, and she be pleased to dwell with him, let him not put her away.
13And the woman which hath an husband that believeth not, and if he be pleased to dwell with her, let her not leave him.
14For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband: else were your children unclean; but now are they holy.
15But if the unbelieving depart, let him depart. A brother or a sister is not under bondage in such cases: but God hath called us to peace.
16For what knowest thou, O wife, whether thou shalt save thy husband? or how knowest thou, O man, whether thou shalt save thy wife?
17But as God hath distributed to every man, as the Lord hath called every one, so let him walk. And so ordain I in all churches.