I’m 51. At 50 I realized that music has always been important to me, that I’m creative and like making things, and it was silly I’d never learned an instrument. So I bought myself a bass and this course.
In full honesty, the biggest challenges are mental, and your style and pedagogy are fantastic antidotes. I’m too old to learn? Never! It’s been a long time since I learned something new? Great time to start! Growth is uncomfortable. Period. Anyone who’s lived a few decades should know that by now, but it bears reminding, and it certainly doesn’t have to be scary. Is it a waste of money? Only if you give up, and even then you can give it to grandkid or sell it at a garage sale next year and be glad you tried something. That equals an investment in yourself.
Buzz lessons have the information a learner needs when it comes up. There’s emPHAsis on the importance of keeping things light and in bite-sized chunks–applicable to a concept or skill–but also to the time needed for lessons and practice. I got a boost when I started picking up my bass for 10 minutes or less just because it was nearby. 5 min before heading back to work, or before making dinner. It wasn’t lessons, but practicing a riff or a drill several times in the day adds up!
The supportive forum is a huge asset, too.
It’s worth noting that learning new things, and especially languages or musical skills, are closely linked to maintaining cognition while aging. Plus it’s a hobby that builds new connections and community.
Fortunately, I don’t have many of the physical challenges, although I sometimes squint at tabs. 
Probably assurances about alternative postures, straps, lighter instruments, short scale options for less finger stretching (it’s not why I have and love one, but Mike Watt said part of his Wattplower design is making it small and light for his oldening body)… there are many accommodations available.
Lastly, a revisit of the gear needed to start would be appropriate. A one-stop guide to options. Illustrations of methods One through Two Thousand. I’ve sketched the concepts out (bass>headphone amp / bass> combo amp / bass> / etc.) several times for confused friends. “Didn’t you just buy an amp? That huge speaker?” “Well, that still needs at least one more box to make it go boom…” And some things are interrelated. e.g. Find more practice time with a couch rig.
There’s a lot to learn, and some of it is tech heavy. I’ve grown up with computers, but others may have less familiarity. And the world of gear options make the endeavor both potentially cheaper, and potentially more computer-y. As far as the course goes, I find the Bass Buzz Web site and lessons structure to be quite user friendly and intuitive. But some UX testing with the agéd couldn’t hurt.
If I’m in some retirement villa in 30 years, I want to shake the pictures off my neighbors’ walls. Not really. But kinda. It’s one venue where half the crowd will be asking to turn it up!
Thanks for making a great resource and continuing to make it better, Josh. Your experience, thoughtfulness, charisma, and approach make it easy and fun.