*pulls out rune factory 4 lore* warning MAJOR SPOILERS.
all the guardians are romanceable, yet because they sealed themselves away to save ventuswill at diff points at time - each guardian extends venti's lifetime by like 20 years, but they were all released at the same time. Keep in mind that Ventuswill is a Native Dragon, literally a GOD. She has a long enough life already and never wanted the Guardians to sacrifice themselves for her sake. She became friends with Leon - he found out that she was dying so he sacrificed himself, and an Earthmate helped him with becoming a guardian (which is why venti was kinda meh with you at first.). Venti tried to seclude herself so the same thing doesn't happen, but everytime she met one of the guardians (before they became guardians) she was charmed by one of their qualities, and them they found out she was dying, and them sacrificed themselves. You rescue them as apart of the MSQ
Leon was the first guardian, idk his age, but he's apparently the oldest out of all the rf4 marriage candidates ignoring the time he spent as a Guardian. By the way he looks, i'm just gonna say mid-late 20s. I'll just say 27, idrk. There are four guardians, Leon was a guardian for about 80 years so technically now, he would be 107. Think of it like cryosleep/stasis. Still romanceable. Also he's hot but we'll ignore that comment-
Dolce was the second one, she's an elf so GOD KNOWS HOW OLD SHE IS WITHOUT BEING A GUARDIAN. But all romanceables are canonically around the same age, early-late 20s.so lets say shes like 23. With the same logic she would be 83, but technically 23 still.
Dylas was the third guardian. Not sure about his age, I'll say 23 too. Apply the same logic of cryostasis/sleep, he'd be 63.
Amber was the 4th and last one. She and Kiel (another romanceable) are the youngest romanceables in rune factory 4, so i'd say 21. So that would make her 41.
All four of them are romanceable, but keep in mind, becoming a guardian is essentially going into cryosleep/stasis(until released by an Earthmate, aka, the player character), so while they may "age" in terms of how long they were alive, they don't actually age until you release them, then they live relatively normal lives (normal in the rune factory universe XD)
Same logic goes for Aang, he went into cryosleep, he was LITERALLY frozen in ice. Like i said, while he may have aged mentally he hasn't aged a year physically.
Holy f**k that was long