It's not retirement at 45 that's not sustainable.
It's policies that encourage people not to work, or maybe to work 30 of 35 hours a week, as well as scare off those who coordinate an economy and make it run smoothly (thus forcing the government to go into ever more debt, and crowding out even the few that would be willing to work) that's not sustainable.
Most people in America do not work 70 hours a week. The great majority of people actually work about 40 to 50 hours a week. In any case, anyone working 70 hours a week and not making a damn fine living is doing so because they made the stupid decision to have kids. Kids are expensive and unnecessary, which is why I decided long ago not to have any.
And no, our current economic model is based on mutually beneficial free exchanges. If I sell you a remote control for $15, then you value my remote more than your $15, and I value your $15 more than my remote. Otherwise the exchange will not take place. That, or you're just retarded.
The system can sustain everyone retiring at 30, as long as they save up and live off their own money afterwards, as opposed to social security, where they would live off somebody else's.
Capitalism is based on two principles that I subscribe to. One is that people would not work if they didn't have to, or at least not in amounts that would make their own lifestyle sustainable. The other is that people need to be rewarded for being smart, hard-working and successful, because the alternative is rewarding them for being dumb and lazy, by shielding from the consequences of it.
Senior executives are people who usually spent ten years of their life in college (which is expensive and no fun) and work 75 hours a week on average. In their shoulders falls the responsibility for the actions of the hundreds of people they command, and if they mess up they catch hell from the board of directors or their shareholders (an increasing number of which are hedge fund managers holding retirement funds for average-joe americans). They earn their keep. They don't steal it. People on welfare can't say the same thing. They sit at home and expect the taxpayer to reward them for their utter failure to make something of themselves. They're not in that position because society has failed them, but because they have failed society.