Generally, in an irreconcilable differences case, long term marriage, 50% is the presumption in my jurisdictions unless there are unusual factors, or unless the parties agree otherwise.
This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.
Colorado is an equitable division state. In deciding what is equitable the Court will look at issues such as the total assets, the contributions of the parties and your earnings. Since your wife has never worked, she probably does not have the same earnings from social security that you have. This is an economic factor which the Court can take into account. It does appear that she is able to work after the divorce and that may balance out the social security issue.
As a starting point an equal division of the IRA is the most likely outcome. However if your social security benefits are a lot higher than what she can expect to earn there may be an argument for her to get an additional share. Since you have provided limited facts you may choose to have a one time meeting with a lawyer who can review the complete assets, income etc.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.