First of all, why is it important how old a political system is? Does that say anything about its quality? Would like to hear what you think about that.
Then: Switzerland
Basically it was a rather loose federation of so called "Stände" (now known as Cantons, i.e. what Americans call states). There were two different kinds of states, independent ones and those governed by the former. In 1815 this was changed by Napoleon to the first Helvetic republic. I think the idea behind it was to make sure that Switzerland remains a neutral place and not mess with the big ones in Europe (there were indeed some people who thought that Switzerland should do that, mess with the big european powers).
In 1848 the current constitution and governmental institutions were put into force, preceded by a civil war were liberal forces beat conservatives (read cities against the countryside or reformists against catholics).
The constitution was written with the American constitution as a basis (hence my question why it's important how old a system is. Because i think the blokes who wrote the Swiss constitution have learned from the Americans and made some points a little bit better. Just my humble opinion, tho.)
Since then nothing has changed, except for one state being created out of a part of an already existing one. And i think the guys did a great job back in 1848, because since then Switzerland has been one of the most stable countries, stayed out of both world wars and has transformed itself from a country of poor peasants who often were forced to emigrate out of sheer hunger to becoming one of the richest countries in the world.