For many people, retirement planning is built around a few familiar ages. Age 59½ is when the normal 10% early-withdrawal tax generally stops applying to retirement-account distributions. Social Security becomes available later. Medicare begins at 65. But what happens if you want to retire at 55? Or 52? Or even earlier? You may have accumulated substantial wealth in your IRA, 401(k), or other retirement accounts but discover that much of your money appears to be "locked up" u