Jack Winters (the Living Diamond), is Emma Frost's fatherJack Winters the Living Diamond from X-Men #40, was an evil mutant with telepathic powers who, as a result of exposure to a radioactive element, mutated even further into a man made of "living, flexible diamond." This power combination, telepathy, combined with the ability to turn to diamond acquired as a further mutation later in life, is incredibly idiosyncratic. What we saw of Jack showed him as a working-class, criminal sort, bank robber and burglar, which fits with Emmma Frost's background as growing up poor and working class. Jack Winters was certainly old enough to be Emma's father, as a balding male when Cyclops was barely post-pubescent (and it is known Emma Frost is the same age as the original five X-Men). The two have oddly similar last names: Jack Winters, Emma Frost.
One of Sunfire's mutant powers is longevity.Sunfire's parents were killed by America's use of atomic bombs on Japan. Assuming he was a baby, that would make him about 67 in 2011, and thus far there hasn't been any explanation of his longevity. Baron Zemo II has a similar origin, although his longevity is explained by regular use of Chemical X. It's possible the atomic bomb reference may be "topical," but 1) thus far all World War II references haven't been topical (with the possible exception of Ben and Reed's wartime careers), and 2) it's something of a defining moment for the character difficult to shift off to a later event like Tony Stark's Vietnam origin.
Wolverine's healing factor requires periodic use of his clawsWolverine's old, uses his claws a lot and doesn't age. Meanwhile Old Man Logan has him being old and not using his claws since the villains took over and aging. Clearly he needs to use his claws to keep his healing factor sharp.
Apocalypse isn't immortal, just hiding his age with the rejuvenation chambers.I find it hard to believe that someone could simply be born immortal, so he's about 85 but the chambers keep him young and fresh.
Alternatively, Apocalypse has Healing Factor related Longevity.
Destiny was infertileIn-universe explanation for why Mystique was originally going to be Nightcrawler's biological father, but was later decided to having Azazel be his father. Mystique's original plan was to get Destiny pregnant as a man, but when Destiny was tested for infertility Mystique sought an alternative solution. Azazel was understandably surprised, but agreed to the deal. 9 months later, Kurt was born.