Lowering the age of marriage will lower the divorce rate not raise it. As singles get older and being unmarried start having unrealistic meshgasim about what they expect from marriage and a spouse, and are then disappointed when their fantasies are unrealized; whereas marrying younger and more innocent before developing those unhealthy expectations will enhance their marriage that they started earlier in their lives.
Look at the Chasidish and Eretz Yisroel divorce rate (where they marry younger) compared to the non-Chasidish/non Eretz Yisroel divorce rate (where the average age at marriage is a bit higher). The former have a lower rate of divorce.