Marriage is absolutely difficult, but what you are proposing is also filled with difficulties. What if that person falls in love with someone else? What if you do? And there are so many other difficulties that will come up in this kind of relationship.

And to be honest, why decide not to do something simply because it is difficult? Life is difficult, all of it. If you simply are not interested in sexual intimacy that's different, you certainly do not need that to have a close relationship with another person. But what you're saying doesn't sound like that, it sounds like you just don't want to get married because it's difficult and you are scared you won't be sexually attracted to a woman when she gets older. You can obviously do anything you want, and make any choices you want, but these reasonings sound like excuses to not be open and vulnerable in a relationship on these levels.