Best driving route from W Coast US to Guanajuato

[DonJuane]

I can't help with driving from the West Coast but because you did mention that the people desiring to visit were in their late 70's, I'll contribute the following for your use or discard.

Make sure they are in shape, there are a lot of stairs here. Also I hope they have driven in Mexico before. When I was younger I could never get coordinated while driving to look left, right, up, down, forward and backward or adding to that, being foolish enough to think I'd be able to watch the scenery as I did so. I've been driving in Mexico for some years now and am not really that much better - still miss about every 30th tope. One day I'm going to miss the wrong one and bend my frame. The suspension is all to hell already anyway. Impossible to keep a fine tuned car here at least in the suspension department.

And before anyone out there famous for pouncing on me does so, this is reality folks. You can come here, you can enjoy the city, you can have the time of your life but be a Boy Scout - Be Prepared. Logically speaking, it probably doesn't matter to anyone else what we personally are able to do physically, it's up to the individuals visiting as to their capabilities. And I don't mean to ruin anyone's trip because you'll do that on your own if you're not prepared. Stair climbing, light aired high elevation, underground driving with no GPS in tunnels and complicated routes around the city, it's not for the lighthearted. So take a challenge or take caution while being prepared.