401(k) plans are not considered to be joint. The owner of the account must meet the exception to the penalty.

There are alternate exceptions that you might qualify for, considering your question -- if you are age 55 or older and separated from service (the job), or "Made as part of a series of substantially equal periodic payments (made at least annually) for your life (or life expectancy) or the joint lives (or joint life expectancies) of you and your designated beneficiary (if from a qualified retirement plan, the payments must begin after separation from service). " (The second option is copied from IRS Publication 575.)

In both cases, you would have to have left your job before taking the distribution(s).

Each of you has separate 401K plans. 401K plans are never joint. Your wife is eligible to withdraw without the 10% early withdrawal penalty. You will not be able to. If you have very large medical expenses (more than 7.5% of your income), are paying medical insurance premiums with it, purchasing a house, or have been laid off and are having hardship the penalty can be abated by exception.