近年來世界各國年輕世代擔任政府首長的新聞時有所聞，彷彿存在著一股政府首長更年輕的趨勢。政府首長作為國家最高領導人，其就任年齡反映了該國政治菁英的甄補與菁英流動特徵，也可能有不同的政治領導風格。不同政治制度下的政府首長若存在顯著年齡差異，顯示不同政治制度下給予有心從政之士的機會與空間將有所不同。本文欲從制度面向切入，探討民主國家不同憲政體制下與不同選舉制度下政府首長年齡的差異，並進一步探究在不同憲政體制與選舉制度的組合下，哪一種制度組合較能夠讓年輕的政治菁英出任政府首長。首先，儘管年輕世代擔任政府首長經常受媒體大幅報導，但實際上政府首長年輕化的全球趨勢並不存在。其次，關於憲政體制與選舉制度這兩種政治制度與政府首長年齡的關係，就憲政體制而言，本文發現總統制比內閣制更能產生年輕的政府首長；就選舉制度而言，比例代表制相比其他選制更能產生年輕的政府首長；就憲政體制與選舉制度的組合而言，總統制與相對多數制的組合，相較於內閣制與比例代表制的組合，更能提供年輕世代擔任政府首長的機會。

Recent news reports of younger people becoming heads of government seem to imply that the age of the political leaders is getting younger. As the chief political leader in a country, the head of government’s age reflects issues pertaining to the elite recruitment process, elites’ mobility, and governance styles. If there is a significant age difference of the head of government in the presidential system and parliamentary system, it means different political systems provide politicians with varied opportunities to become the head of government. Adopting an institutional perspective, this paper asks if there is an age difference amongst heads of government in democratic countries with varied constitutional systems and electoral systems. If so, what kind of institutional settings favor young political elites to become the head of government? The findings show no evidence that the age of heads of government around the world is getting younger even though such kinds of news have often been reported by the mass media. In terms of the relationship between age and political institutions, i.e. constitutional system and electoral system, a presidential system offers more space for young political elites to become heads of government than a parliamentary system. The proportional representation system gives young political elites more opportunities to become the head of government than other kinds of electoral systems. By taking the constitutional system and electoral system into consideration, a combination of a presidential system with a plurality system enhances the chances of younger people to serve as heads of government than the combination of a parliamentary system and proportional presentation system.

政治制度；憲政體制；選舉制度；政府首長；年齡