There is something to say about the difference between a long term relationship to an Old person versus and Older person.

With an Old person, the decay has already begun. You can see and observe quite tangibly that they're on the decline and make some educated assumptions about the amount and quality of time you're going to have left with them. Generally speaking, you're going to have a pretty good idea of what you're getting into with the relationship and you're willing to take it on.

With an Older person, they're still relatively spry, relatively flexible, relatively healthy looking. Often these people fall under the rough category of "Middle aged" (which I place pretty much between 35 and 55, though I'm aware that it's no longer a very solid description). While this might betray some physical changes for the worse in women (wrinkles, sags, etc), in men it is often the prime of life: they may not be quite so fast or strong as they were at 20, but they're at peak attractiveness for a lot of other reasons. Usually, while they might be exhibiting some health problems, it isn't yet clear if there are going to be a lot of problems later on.

And there's the rub: much like being with a younger person (30-) and Older person is a gigantic question mark, but they are also older. The 25 to your 25 has, without medical conditions and lifestyle taken into account, about the same expected life span as you. The 45 to your 25 is a gigantic question mark with a little -20 written next to it.

In case I haven't mentioned it earlier (forgive me laziness, but I don't feel like going to check) my husband has twenty years on me. He has health problems that are becoming increasingly apparent the longer we stay together and I worry both for him and (honestly, selfishly more) for me.

I don't think it's wrong to be worried about yourself (in this case, myself) in regards to a relationship, but I still feel slightly guilty. I guess that's my Id speaking.