This is referring to http://www.darklegacycomics.com/230.html.
Narya drank the fountain of youth enough to bring him down to "teenage years", say 18. Assuming Miji was born in the year that Harry went back to Gnomeregan, then the present-day Miji should be 52 years old, thus meaning that Narya drank to his teenage years when Miji was 49 (52-3). Lets say he drank himself down to 18 years old. That means when Miji is 52 years old in the present, Narya is 21.
"Harry" goes back 52 years into the past. He is his 21 years old self, and Miji "should" be 0 years old or so. Given recent comics, young Narya has to look a lot younger than Harry, yet barely older than Miji. Remember young Narya hasn't drank from the fountain of youth yet. You can see now that if Narya's age difference was too big (say 30 years older) than Miji without the fountain of youth, then young Narya would be 30 when Miji is 0, even older than "Harry" who is at 21. Since this is an obvious contradiction, the only possibility is that Narya's age is between 0 and 21.
Basically, Narya can only be 21 years older at most from Miji originally, but even then would be stretching it since he looks much younger than Harry. So I assume Narya is 5-10 years older than Miji. This is further supported by #398.
Anyways, in all the recent comics, Narya looks like he's only a couple years older than Miji, which is rightfully proven. I have no idea how much older Narya is in his bearded-age -- he could be younger than Miji at that time -- however, at his pre-fountain age, he looks to be A LOT older than Miji, with grey hair and the like, despite only a 5-10 years difference. That's my biggest question: 5-10 years difference, yet pre-fountain Narya looks unfathomably older later on. Huh!?
(One more thing is that Harry has been keeping his hair dyed blue even though it's greying out? Since he is definitely older than pre-fountain Narya, we would see grey hair now, otherwise.)
Just some thoughts.