Unfortunately age is only not so much of an issue as you get older. In my 20's and 30's I would have been horrified at going on holiday with a group of people who were all 50+, as I would have seen this as going on holiday with my parents or grandparents.
JY from what I have read online, aim their holidays at the older generation - this is what they stated in feefo and I couldn't find anything relating to the age range on JY's website. The fact that more and more younger people are looking for safe ways to travel is great as I really like a mix of all ages. Perhaps the reason why JY don't mention the age range on their site is because they are looking to expand their portfolio to attract all ages... but if I was a younger traveller I think I would be asking the same question - what is the age range.