I'm only inclined to generalise when I've good reason to.
The libertarians that I've known who do not speak as though the possessed objective truth havent ever suggested that they are an ideology among many, at least not in the sense that their ideas are a social construct and only liable to prove practical if enough people agree to suspend disbelief and ignore the short comings in fact of their theorising.
So I generalise from what I've experienced, sound empirical observation, perhaps you're anomalous in this respect.
Given what I know about US politics I'd have thought it would be young republican and old democrat, if this quote is meant to mean that young people are radical and aging leads to moderating of perspectives.
Democrats in the US could only be considered radical or utopian and republicans less so if you accept a fundamentally conservative framing of the debate about radicalism and moderation. I'd suggest that in the US, and probably the world at the moment, the right wing is the only radical movement with a vision for total or revolutionary change. The left is running to stand still and chooses to campaign the most on single issues which are unlikely have the impact of the right wing vision if it ever realised or successful.
In terms of illusions or enchantment and disillusionment or disenchantment, it could happen in the case of either left or right because they both have shared fantasies, visions, value statements which are beyond anything that will ever make practical policy. It should happen in the case of the right wing because its happened years ago on the left wing, there's never been a comparative development on the right wing. Perhaps its to do with intellect or temperament I dont know.
The problem with libertarianism is that the term is too broad. It refers to everything from classical liberalism to near anarchy. Some libertarians are much more extreme than others. I consider myself libertarian, but I would never support the elimination of public roads, parks or libraries. A big part of it for me is the concept of federalism. Perhaps a service should be offered by the government. The question is, which one? Why should a service be pushed on the entire country that can easily be handled more efficiently at a state level? Especially when it's something where the federal government's constitutional authority in that area is questionable. What constitutional basis is there for NASA? Or for the Department of Education? Or for the USDA, or the FAA? Why are these bureacracies necessary, and if they are, why have we not given the US government legitimate authority over them?
I straddle the line with minarchism, a finger each in anarcho-capitalism, moderate social liberalism and moderate fiscal conservatism. As you can see, political philosophy within my brain is like cage fighting! The economics overview is what usually sways me, although try as I might to ignore or rationalise them away, social aspects also impact.
If God had given you property rights, then you would not need the government to enforce or even allow them -- they'd be self-enforcing. Property rights exist only to the extent that they are protected by force from those willing to violate them -- beyond that it's an empty concept.
I know right? Property rights are not innate or God given, in fact some societies didn't believe in that concept at all, many Native Americans believed that land could not be owned.
"Sentiment without action is the ruin of the soul." - Edward Abbey