False. Dimaria and Gray were never together on the same battlefield at the same time.
Gray was deployed to defend Southern Fiore, which consisted of Dimaria in the ranks. However, being in the same region does not equate to the same battlefield. We never once see them cross paths, neither was it implied Gray and the rest were affected by Age Seal when Dimaria employed it. Let's not get too carried away in overhyping the spell. It is unlikely Dimaria's Age Seal even possess the same AoE as someone like Wahl, when she incorrectly surmises the range Wahl's attacks were capable of.
While it has never been stated how huge is Southern Fiore, the distance from the port to FT guild hall is a good 370km apart. And baby, that would mean it could fit a State from New York to Washington. Which really isn't anything to be surprise about as Fiore is a goddamn country, and Magnolia is just a city. In addition, the characters and battles are dynamic. It is erroneous to assume Gray and Dimaria were in the proximity of one another.
Brandish's spell also worked on Natsu too. It could work on Natsu and Gray because they were not as strong as they are now. Fairy Tail is a series. A series where the characters grows and develops steadily as the story progresses, be it in a good or bad way. That is another topic to discuss.
Gray and Natsu are stronger than they were when they were left astounded by Brandish's magic power during her introduction. Mashima went the extra mile to show us how much the tables have turned when Brandish and Dimaria were unable to comprehend Natsu's strength in his fight with Neinhart, and when END awakened for the first time, respectively.
END is an Etherious. An Etherious is driven by the single-minded inborn desire to kill Zeref. Natsu at the point of time was that.
Holding back? Ludicrous.
Gray was stalemating Natsu here. Not willing to concede this point is blatant downplaying. We don't know how much of an slayer advantage does Gray has here, because it is not clear how far has Natsu demonized here. Regardless, most of their exchange here was CQC and melee. Neither of them was seen busting out their strongest techniques against the other.
Gray has grown from molding static ice creations with both his hands, to instantaneously freezing Natsu's flames with a swipe of a hand. And telepathically separating his ice then freely control it in mid-air to direct them towards his foe. Neither of them was able to wound the other despite landing hits. Natsu was like the flat track bully he usually is, overpowering his way out with brute force. Gray was actually outmaneuvering him.
And this is the Gray who was already wounded after his fight with Invel, running mostly on adrenaline. This, however is a how traumatised a fresh Dimaria was after getting brutalized by Natsu.
Age Seal has her limitations. It is not the be-all, end-all as some choose to believe. Otherwise we wouldn't have seen Dimaria employing Age Seal so quickly in almost all her fights. Nobody can be that daft to do so. The move she actually kept and only employed it when Age Seal was negated, was her Chronos soul takeover. Unfortunately we have fighters here who can overcome her strength in that form.
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(she would use TS b4 August can even react) 
