One of the misconceptions of those that are unmarried and in ministry (or out of ministry for that matter) is that singleness is a cause of immaturity. Although, there may be times when this is true, it is the exception rather then the rule.
Let me challenge you with this thought: Maturity is the result of a process and not a specific event. How this relates to our conversation here is that the event of marriage is not necessarily a sign of maturity. Maturity is developed, it does not just happen.
With that said, a single person in ministry should be just as mature as one which is married. Although some of their experiences may be different, they have both had the opportunity to work through the muck and mire of life and to emerge on the other side stronger and more mature.