In BG2 you can find his full plate armour and shield, and in BG3 his helm is medium armour and he wielded a greatsword, he's definitely supposed to be a John Baldur fighter type. That said:
1 - Nothing in his lore suggests that he was a
great fighter - he was famous as a leader, explorer, and trader. He could have been, in D&D terms, a level 3 fighter / level 10 merchant who could just afford top-tier enchanted armour and weapons because he was filthy rich.
2 - Dark plain clothes with a face mask and hood are simply the correct outfit for dramatically brooding on a rooftop, regardless of your main class. You'd look like an absolute tool trying to strike a Batman pose in full plate or wizardly robes.
Also, I don't think he needs to be particularly old; Christopher Columbus did all his four trips to America between his 40th and 50th birthdays. Balduran is said to have started voyaging as a young man, and he only visited Fantasy Caribbeans once (the second time was his disappearance voyage). He also didn't oversee the building of the city or anything, he just donated a bunch of money to build a protective wall around his old village and then fucked off again. All in all, I think a late-40s Balduran is perfectly reasonable.
There is also key evidence that he was white:
Balduran held the memory of his mother dear. On his 18th birthday, she gifted him a set of cutlery that the man cherished. The butter knife of Balduran that was discovered in the mid–14th century DR was a part of the set, and the rest was stored in Balduran's lair underneath Baldur's Gate.[3][1]
Obviously he could not have been from a lactose-intolerant race.
(Also, interestingly, the FR wiki de-gays him as well. Good job, editors:
At some point in his life, Balduran befriended the glittering bronze dragon named Ansur. They formed an intense bond, marked by shared adventures like their quest for Yal Tengri's Great Spire. Ansur willingly endured hardships to stay by Balduran's side, cherishing their shared experiences. However, this bond was strained after Balduran's transformation into the Emperor. Ansur, seeking to cure Balduran's illithid condition, called upon various healers in a spirit-breaking effort, which ultimately soured their once-close relationship. Ansur became convinced that the Emperor needed to be "cured"—despite its insistence to the contrary, and ultimately tried to give it a merciful death. The attempt failed, and, in the ensuing fight, the Emperor cut Ansur's life short.
As of the Year of Three Ships Sailing, 1492 DR, the helm of Balduran resided in Wyrmway, beneath Wyrm's Rock, safely hidden behind the lifeless body of Ansur, Balduran's once close friend.[1]
)