My father-in-law never drinks. I don't think he has drunk even as younger, unless there are so bad stories to tell, we haven't heard. You can always count on him being sober to drive... Everybody knows this and doesn't offer him anything. There's nothing stronger than home-brewed beer what they offer at their house, but he is tolerant of others drinking elsewhere.
My mother-in-law does drink, if there is an occasion, when drinks are offered, but she can't control her drinking very well. She made an ass of herself at our wedding, when she started drinking the homemade wine and didn't realize to stop. The video clips from our wedding are priceless.
I only like social drinking amounts myself nowadays. If there are sober people present, it's even more desirable to abstain from drinking too much.