Since youth is fleeting, old age sucks, and death is always right around the corner, the speaker urges the virgins to make use of what they have ("use your time") while they still can.
In other words, don't be "coy," meaning shy, reserved, or inactive.
The speaker doesn't just encourage the virgins to "use" their time, but to "go marry" (as in, to go get married!) while they still can.
So this whole time – all that stuff about death being close, youth being short – the speaker's been gearing up to talk about marriage? Yes indeedy.