Age is meaningless, he’s only four years older than Blackbeard who’s going from getting one-shot (along with all his crew) by Shiryu’s equal to being the potential strongest character in the series.
All I’ll say is it makes little sense to judge Shiryu before he’s really had a chance to shine. There’s a reason that Blackbeard was put in the Owrst Generation, it’s because he and his crew are still rising in power. They’re a very different type of character to Mihawk, who was introduced at the top and with no need to grow
Black Beard wasn't added to the WG because of his crew but rather for his own merits. Or did they add Zoro to the WG because of Luffy's crew too?
He is going to be a hell of a threat but I still don't see him being Zoro's last opponent. Before the time-skip BB alr had the Gura, the Yami and a fairly good crew; now add maybe a new fruit that will boost him even more and there you have, op antagonist.
My point is:
-Shiryu was ≈ to Magellan. Add a time-skip of 2 years were he could get some mastery on his mediocre fruit, CoO, CoA and a stat boost. Those things wont make him jump from Magellan level to Prime Ray level.
-BB was alr very strong before the ts till the point where he trash talked Ace, a YC3. Now add on top of that a 2 year time-skip, the Gura, maybe another df, ACoC, CoA, CoO and a stat boost. Those things could rlly make him jump several tiers.
I rlly don't see how a suke, basic haki and some stat boosts can make you go from being ≈ to Magellan to being ≈ to Prime Ray in 2/3 years.