While he has said repeatedly those near retirement wouldn't be affected by changes, it's not clear what age he means. In the January debate he said it was 55. In his latest debate with Obama, he said 60.
Romney has not said much recently about whether he supports individual investment accounts tied to Social Security. In his 2010 book, "No Apology," he advocated for voluntary "add-on" accounts in which workers could choose to contribute 1% of their wages to their own account. Workers who didn't want such an account would have to actively opt out.