For sure. If you're unattached, tickling opportunities become fewer once we enter into adult life. If you look at it from a numbers perspective, it makes sense. While we're in school, we're surrounded by hundreds, even thousands, of people our own age. And it's during a time when openly being playful and flirtatious is quite common. Playing 'kissing tag' in the workplace is more than frowned upon. But during grade school, such activities are normal. As we age, the types of activities that we engage in that can provide opportunities for touching and tickling become less and less, because they become less and less acceptible.
In my own experience, once high school ended, it was like... Shoooom!, tickling reached extinction levels compared to the frequency it had been occurring. And it just got more infrequent from there. Something that I had going for me that disappeared about the same time was my "built-in popularity". I was a preacher's kid growing up, so everyone at whatever church we were at knew me. A year after I finished high school, we moved away and my dad took a break from pastoring. Suddenly, I was just like any other 19 year old. I didn't have a reputation preceeding me so to speak. No one really cared who I was. Add to that my bent toward introversion, and it was a recipe for a social (and tickling) wasteland. Not that I knew it at the time, but looking back, it's quite apparent.
But that's just my experience. There's probably someone here who will say their tickling experiences actually increased when they got older. There are so many things that contribute to what each of us experiences in life that no simple explanation will do for all of us as to why something is the way it is. Our experiences are way too nuances and complex for a one-size-fits-all answer. But there are still some things that are common experiences for all of us, and fit within the framework of what it's like to get older. ie... kissing tag is okay when you're 8, not so much with your co-workers when you're 25. And tickling, and where it fits in as we get older, also has a similar pattern of acceptance. As we get older, it's right and appropriate that we make good decisions about how and with whom we will physically interact. If we're acting as we should as adults, the natural outcome is, unfortunately, less tickling. And yes, that sucks.