I'd argue that you can ride a bike into very old age with they right gears, so I don't see the attraction for a geezer. Just ride slower, less far and with people at your level. I can't ride with the fast group on the Saturday ride any longer either.
That said, if this gets people to bike who otherwise wouldn't, more power to them, especially if it is for transportation. I have seen it make a difference on commute routes with people now riding who would not be able or interested to ride otherwise. That's good, every car off the road is a win.
Mountain biking serious trails and peaks, these things just make me sad. Its like climbing a mountain in Europe and when you get up top, you meet the people in flip flops and heels who took the tram.
I agree with JYL that there will be rules required and enforced soon for these things to take the road and not the bike lane. I have had more than one dangerous situation getting passed with a 15 mph delta on a multi use trail I
specifically chose to ride to get away from MOTORIZED traffic. Ugh ...
G