I started doing these trips when I was 31 and at 42 have notched up 20 holidays. The age question crops up a lot and I think it really depends on your attitude to age. Although on a few trips I have been the youngest - it hasn't affected the trip at all, in fact I think the older a person is, the more relaxed and happy they are in themselves and less worried about what other people think of them. They are more likely to sit back, relax and enjoy the trip. Of course this is a sweeping generalisation and there are always exceptions.
I have noticed that JY is attracting a younger clientele and regularly have a wide range of ages but the majority still tend to be in their 50's. As long as that doesn't bother you, I would say go for it. The touring holidays in the main attract a slightly younger age range as they are very active with lots of early starts, so the New England trip is a good one to start with.
One last thing - think of it less as a 'singles' holiday - you will find many married people (Nixon is one example) who love to travel but their partners don't. What you get is a group of like minded travellers who start out as strangers but from day 2 become a close group sharing fun and great experiences.
I think you should take the plunge and book the holiday - you are guaranteed not to regret it and will be looking to book your next one as soon as you return!
Sally