All beer changes over time.
The first major profile to change is the hops. Their floral characteristics fade within weeks. Their bitterness will be gone in a year or two. Also, bottling is a beast of its own. When you bottle, yeast are still alive, and they create an ecosystem of their own, adding alcohol, adding CO2, etc. Those things change the flavor immensely.
Although I won't get into exactly how careful you have to be doing this, I will tell you it is possible to use something like a Sodastream on your beer. Like I said, CAREFUL, but if you taste a beer once, then give it a quick shot of CO2, and let it rest for 15 minutes, then taste it again, the aroma will be transformed so much that you'll think it's a completely different beer.
So, time means not only are some of your ingredients' flavors fading, so the malt will come forward again, but yeast byproducts are multiplying, and your CO2 levels are changing as well.
Since most stouts tout a sweet profile, allowing the hops to subdue means there is going to be a point in time where the balance of hops:malt will be perfect for a particular person's palate. Not everyone will agree! I like imperial stouts with lots of hops. My brother in law likes ambers. His wife likes traditional stouts. Give us each an Imperial Stout, and I'll like it fresh from the brewery. My BIL will like it in a couple months, and his wife won't like it for a year or more. It's all just a matter of opinion.