Well I did two JY trips last year (Americas Golden West & Treasures of Andalucia) and found everyone very friendly.
Both trips were certainly quite hectic with all the excursions we just had one day to chill out in Andalucia but some people got together and went into Malaga on publictransport.
There will be a tour manager with you and I couldn't fault either of the one's we had.
Age range on both trips was 20's to 70's.
I can only say I enjoyed both holidays and have two more booked this year.