I've done 4 JY days and from what you say I think a JY holiday will suit you.
The majority of travellers are normally between mid fifties and seventy, with a few older and younger. On average the ladies outnumber the menaround 3 to 1.
Remember everyone is there for the same reasons, travelling solo, want a good holiday, etc. In my experience everyone gets on great and as a very good time thats why many of us book again with JY.