IRAs have huge tax-advantages. You'll pay taxes when you liquidate gold and silver. While volatile, "the stock market has never produced a loss during any rolling 15-year period (1926-2009)" [PDF]. This is perhaps the most convincing article for retirement accounts over at I Will Teach You To Be Rich.
An IRA is just a container for your money and you may invest the money however you like (cash, stocks, funds, etc). A typical investment is the purchase of stocks, bonds, and/or funds containing either or both. Stocks may pay dividends and bonds pay yields. Transactions of these things trigger capital gains (or losses). This happens if you sell or if the fund manager sells pieces of the fund to buy something in its place (i.e. transactions happen without your decision and high turnover can result in huge capital gains). In a taxable account you will pay taxes on dividends and capital gains. In an IRA you don't ever pay taxes on dividends and capital gains. Over the life of the IRA (30+ years) this can be a huge ton of savings.
A traditional IRA is funded with pre-tax money and you only pay tax on the withdrawal. Therefore you get more money upfront to invest and more money compounds into greater amounts faster. A Roth IRA you fund with after-tax dollars, but your withdrawals are tax free. Traditional versus Roth comparison calculator. Here are a bunch more IRA and 401k calculators. Take a look at the IRA tax savings for various amounts compared to the same money in a taxable account.
Compounding over time will make you rich and there's your reason for starting young. Increases in the value of gold and silver will never touch compounded gains.
So tax savings are a huge reason to stash your money in an IRA. You trade liquidity (having to wait until age 59.5) for a heck of a lot more money. Though isn't it nice to be assured that you will have money when you retire? If you aren't going to earn it then, you'll have to earn it now. If you are going to earn it now, you may as well put it in a place that earns you even more.
A traditional IRA has penalties for withdrawing before retirement age. With a Roth you can withdraw the principal at anytime without penalty as long as the account has been open 5 years. A traditional IRA requires you take out a certain amount once you reach retirement. A Roth doesn't, which means you can leave money in the account to grow even more. A Roth can be passed on to a spouse after death, and after the spouse's death onto another beneficiary. more on IRA Required Minimum Distributions.