Excellently phrased. Looking for a husband?
Nah, really I think the point is not a question of "fun" vs "serious," although that is what the OP tried to set it up as.
The question is really a matter of how many people can have fun while being serious. I really do get a great deal of enjoyment out of discussing the Bible and talking about people's experiences with God; talking about their desires for a family (or not), discussing their beliefs and relationship with God..... These all CAN be fun, but also quite serious.
Many christians I know define "fun" quite similarly to non-christians, maybe not explicitly sinful but certainly flirting with sin in many cases. It's about finding a way of turning your brain off and embracing frivolity, often accompanied by pleasure. With very few exceptions, pleasure has always seemed to be a thing of this world, and we're called to not conform to these. Whether this "fun" is legalistically sin or not, frivolity is not the only way to have "fun/be playful." IMHO, there are many more beneficial means of being both fun and serious. I would encourage people to seek fun through seriousness; I know it is possible and have seen its benefits.