There are some really neat bikes of that vintage. But something to consider with that old of a bike is that some of them had problems back then. Manufacturing and engineering has worked a lot of kinks out in the last 35 years. While the bike may be in good running order, I think most people would agree that the chances of you running into problems with a 40 year old Honda are much higher than with a 4 year old Honda. The last thing you want when you are a brand new rider is to be distracted by turn signals that don't work or a clutch that slips. If you have zero riding experience, I would do the following:
1) Go take a motorcycle safety course. They usually use small standards such as a Honda Rebel or a Suzuki TU250. You will get a day or two of riding time out of the class. Granted, it will be on a closed course at less than 20mph, but you will learn the basics of how to operate a bike.
2) Go buy the same bike or similar to the one you use in the class. Stick with something in the 400 pound range or under, and one that is low enough for you to put both feet flat on the ground. Make sure it is in good working order. Those little bikes are great starters and you can often find them for a couple grand or less. After you get a year or two under your belt, now you can start thinking about getting a bike that is more suited to your liking. Chances are you will drop your first bike a time or two anyway. I did. We all did. It happens. WAY better to drop a starter bike than a brand new machine.
3) Go buy really good gear. A good helmet, gloves, bright colored jacket, pants, and riding-specific boots. Do not skimp in this area. You are probably looking at $500 or so to gear up. If you thought motorcycling was cheap, think again. There is a saying..."Dress for the crash, not for the ride." Also, an achronym is ATGATT...All The Gear All The Time. That one time you decide to run up to the store in shorts and a t shirt is the time you will end up with your skin scraped up and down Maple St. You will hear about guys who choose to ride without full gear. They have that choice, and they know the possible consequences. They have been riding for a long time. You have not. Consider it the difference between the way a 6 year old should gear up to ride a skateboard as opposed to Tony Hawk.
4) Go ride, by yourself. Start at slower speeds during non-congested times. In your neighborhood, through back streets, or anywhere that is off the beaten path. Don't try to take on the world during rush hour traffic on busy highways with a whole lot to keep track of right away.
I don't want to scare you, but know this...I am just now considering getting back into riding after almost 3 years away. The last time I rode I ended up staring down a cliff with a broken shoulder BECAUSE I WAS TRYING TO RIDE SOMEONE ELSE'S RIDE AND FOUND MYSELF IN ABOVE MY HEAD. At the time my pride wouldn't allow me to admit it, but that is the truth. Things happen really fast on motorcycles. Your mother's concerns are valid. She doesn't want to bury her son. Take every precaution that is given to you. The world is full of guys who were too cool to heed good advice. I was one of them, and lucky to live to tell about it