Hi Stevie
I completely understand where you are coming from. You actually sound a lot like me as well. I very much prefer taking in the culture than the clubbing scene, though I do like to have a drink or two or three, sometimes in the evening.
It took me about five years to pluck up the courage of going on a solo holiday. I'm 32 and having gone on my first solo holiday last September my only regret is not doing it sooner, as there are so many places that I want to see and explore, that I could have done with those five years.
I did the same as you looking for a short short haul and I escaped to Sardinia with JY in September, and had a really good and relaxing time. I found that I was able to mingle when I wanted or sit on the balcony or laze by the pool doing my own thing. The main thing was that I was not eating on my own - which was the primary thing holding me back for five years.
Now I have done it I have two tours booked for this year - Athens & Corinth Coast in May, and Discover Sicily in September, and instead of being anxious, nervous and excited I am now just excited. I cannot wait to see some of ancient Greece and having a nose to see what Etna is doing (hopefully she is sleeping), and I am saving for my first ever long haul experience in 2018 which I have narrowed down to either India or China.
I suggest that you just go for it. Don't worry about the ages of other travelers, whilst a large portion will be considerably older you'll find there is a wide range, and everyone is a) interested in the place your going, b) a solo traveler who is or has gone through the same thing.
For a first short haul, I reckon any of the Italian, Greek, Spanish or Croatian destinations would have all the sights to see. Madeira also is a very beautiful friendly island to visit with its very own unique culture and climate.
Chris