If you want to know how hard it will be, how about putting some weight on your bike and then riding 70 miles up and down a few hills to see how you like it?

There is a serious difference between what I can do and what I find enjoyable. On my most recent tour, I rode 91 miles one day. This is what I can do. But, putting out that kind of effort every day would not be something I would find enjoyable.

Assuming you are taking highway 1 all the way north, you will have a few serious climbs. One I have done is just north of Jenner and I needed low gears to get up it. But, I'm 20 years older than you.

If you only have one gear and you can't power the bike in that gear your only choice is to walk. Are you prepared to do this?

Ray