@Jack70, sometimes when times are slow, it's tempting to lower your price or take bookings from less than ideal guests.
Personally, I would not allow a large group of young guys to stay in my house. It's just inviting trouble. I have learnt this from having young male housemates over the years. They can be lovely, polite, well brought up people and they always say, yes of course they will follow your house rules. But then they don't and most of the problems arise because they constantly have groups of friends round. In general, partying is more of a priority and when they are having fun with their friends, they don't think about the consequences. The friends don't think that this is someone's home, but rather 'Isn't this a great place to hang out/party!' This doesn't make them bad people, it just demonstrates a lack of maturity.
I had one lodger who asked if it was okay to have a few friends for brunch while I was away on a trip. I said of course. Even though he tried to clean up all evidence, the minute I got home, I knew there had been a party. It turns out his 'brunch' with a few friends had involved 30 people, a DJ with a full on sound system, copious amounts of vodka and class A drugs. Not cool.
This week, I got a request from two very polite 16-year-old boys. They seemed lovely and would probably have been fine (I travelled with my friends at that age, including staying in someone's apartment in Florence), but did I really want to take the risk of hosting two high school kids? I decided no.