This is my response to someone else about the same question that I made a few weeks ago:
I'm in your boat as well with a 12 year age difference. Because of this plus income difference (he's been able to put more into his 401-K because he earns more and my job had a limit on what I could put in) there's about twice as much in his accounts than in mine.
But I'm not worried about it. Using the 4% rule as a general guideline when we retire, as long as we are looking at the entire portfolio when calculating how much is safe to withdraw in any one year I think it's fine to then take that money out of just one person's account.
For example, say things go on for us as they are and it continues that about 30% of the retirement savings is in my name. At retirement we could potentially have about $1 million total. Using 4% as a withdrawal amount, that's $40,000 the first year. That money can easily all come from accounts in his name, after all, he will have $700,000 in his name while I'll have $300,000 in mine.
Does that make sense? It doesn't matter how much is withdrawn from which account at this point, so long as the portfolio as a whole is taken into consideration.