I don't believe there are [any discussion on Leopold von Bergliez's age].
I personally headcanon Leopold to have been born on July 30th, 1136. For reference, this makes him 44-45 pre-timeskip, ~47 during Hopes and 50 post-timeskip (in VW/SS, at death).
There is no concrete evidence to support this, though. He needs to be at an age where it's reasonable for him to have had two kids by 1163. I think it's believable for a Major-Crested noble to be pressured into having multiple kids early, let's say before age 30, and let's say he had none before 18. If he had Caspar sometime in his 20s, and his first son a few years before that, Leopold would have to have been born between 1133 and 1143.
The higher end of this range works best, as Leopold succeeds his father in 1168. He is a man in his prime who has likely started to build his reputation of Adrestia's strongest and an incredible leader. Having Leo be born in, say, 1143 means he would only be 25 by then: given the weirdness of Leopold not being the default heir off of his Crest alone, the further back you go, the more experience and influence he would've been able to gain, making his father's reluctance even more jarring with each year.
Since [this conversation] started from his wrinkles, I do want to mention that I think Crests accelerate their owners' aging the stronger they are. Obviously multiple Crests are the worst in this regard, then single Major Crests and single Minor Crests. Just my theory, but I think it's more reasonable than having dual Crests turn on accelerated aging like a switch. This would justify him looking so wrinkly compared to, say, Alois, who would be eight months older with this birth date.
For the record, I do think he and Waldemar parallel Caspar and Linhardt in their birth dates as well. I don't have an exact birth date for Wal yet, but he was definitely born in the same year as Leo.
Oomf asked me on Twitter but may as well put it here too
TL;DR I think Leo is 47 (born in 1136) in Hopes and I headcanon he was specifically born on July 30th
#fe3h #threehopes #leopoldvonbergliez #countbergliez