Most people walking the Camino de Santiago stay in the most basic of cheap hostels and don't complain about the standards. Always depends on your own (their own) expectations... hostels probably wouldn't be the best idea for a honeymoon, for example!
A lot of Hostels nowadays are no longer "Youth Hostels" but simply "Hostels", providing basic accommodation at a reasonable price. Many will have private rooms as well as dorms to choose from. The StayOK hostels in the Netherlands are a good example. I have been in one of their hostels and it turned out they were hosting delegates from Medicine sans Frontiers for a conference held there - so definitely not just 20-somethings but people preferring to spend their money where it's needed rather than for hotel luxury.
I'm in a hostel right now (my 20s being a distant memory). First night was quiet, second rather rowdier, but I was so tired I went off to sleep anyway. Both mid-week nights.
There are good hostels and bad, Read the reviews.
You can get private rooms in hostels these days which are grand.
If it doesnt have its own jacks and shower though im out. I was in one in France and i had to get up and get dressed to walk down the corridor to the toilet. And when I got there the toilet was disgusting. Then in the morning i went into the shower and there were plasters in it and scum from the person who had just been in. I walked straight back out. Put me right off taking the chance again.