First of all, DeMarcus Ware is not getting younger (and may not be back). Second, their youngsters may not develop as fast / struggle when given a bigger role. There is no guarantee that because they were great this year, they'll be as great or even better next year. The three best defenses of the past 30 years (85 Bears, 00 Ravens, 02 Bucs) all took a step back the following year (and the Seahawks too). They were still very good (and in the case of the 86 Bears great), but they did not play as well as they did the previous year. (Good) NFL teams will adjust based on what they've seen and give them more trouble.
Just because they dominated this year doesn't mean that we have to piss our pants looking at them. Do we have to improve in order to beat them? Yes. But think about it, we played with a banged up team in November in Denver and still put up 24 points. We played with no offensive line in the AFCCG and were still one missed PAT away from tying the game at 20 points apiece. If we can get our offensive line to buy Brady 2.5-3 seconds of a clean pocket and get a running game that can keep them halfway serious we will beat them.
And, if we stay healthy at a decent rate improve on backup LB and #2/3 CB (depending on how one looks at Logan Ryan) we could be right in the mix for the title of the best defense in the NFL.