Welcome, BreezieD. I like your user name.

Yes, WOWZERS on 40 miles for your first ride! And, yes, you must already be reasonably fit.

I assume you intend to ride shorter rides during the week? If you can do 40 for your first ride (even if it was hard), then around 20 should be reasonable for weekday rides. For a long time 20 or so was about my shortest ride distance. However, when I started doing more interval and speed training, the distance was sometimes less as the focus was on intensity. But you need to focus on building your base right now. Just get your body used to riding a bike. The more base miles you get in at a comfortable pace, the easier all your rides will be and the easier it will be to transition to more intense training, if you choose to do that later.

Again, welcome to the board. Welcome to the wonderful world of cycling, and feel free to ask questions any time and share your stories, even if just small accomplishments. We like it all!