Before you comment, please READ the whole thing. Or you will be wasting your time. I tried keeping the post as small/concise as I could
We all know Hiruzen was 69 when he died.
Now during the kyuubi attack, he was (69-13)=56, his looks were different back then, he had black hair and was slightly taller. Even though he was old, we wasn't suffering from old age. If you look at Jiraiya when he died, he died at 53. So his age was very similar to hiruzen's during the kyuubi attack. Yet when Jiraiya fought Nagato, his abilities were not at all affected by old age. He was as good as he was in his prime. No one can argue a 30yo Jiraiya was 10 times stronger. In Naruto, a ninja is hardly affected by old age especially in their 50s..(Orochimaru, Tsunade, A)..they are almost as good as they were in their so called prime. In fact they get stronger during that age(Onoki got faster). So during the kyuubi attack, Hiruzen was pretty close to his prime to say the least.
What he did against the kyuubi was not at all bad, he drove the kyuubi out of the village. However, he was not able to fight it off and at one point he was on his knees about the get hit by the tbb. that's when Minato came into play and teleported the beast.
Now 3 years after the kyuubi attack, hiruzen still fought Orochimaru and defeated him fair and square. he was 59 at that time. The point is, when those anbu members said "HE DOESNT HAVE THE RESERVES OF CHAKRA HE ONCE HAD" they were referring to Hiruzen from 10 years ago when he actually had more chakras and better health.
Hiruzen had a long array of techniques in his arsenal, but he never was godlike strong like Nagato, Madara or Hashirama for that matter. Heck even Hiruzen himself said and I quote" you can destroy me, but a stronger hokage will take my place and defend the hidden leaf village" and he was thinking about Minato(showed flashback). implying Minato was stronger than him. "Prime Hiruzen" is not 100 times stronger than the 56yo Hiruzen that fought the kyuubi. He had to rely on Minato during that attack.