You should just say that directly then. Something along the lines of...
"Us founders are blitzing 80+ hours a week. If you're young and energetic, come join us. However, we'd also like the wisdom and experience of someone more senior. We understand you have a family and will need more life balance, and we're very cool with that."
I'd find that refreshing in a job ad. I'm 42 with a family, btw.