AC97
"@Background Pony #4A6F":/pony/season-9-discussion-thread-warning-spoilers/post/4490878#post_4490878
Not really the only way. If Star Swirl the Bearded survives the finale (guessing he will), he can very likely cast age spells (I think it's pretty much explicit canon that he can), and I think you'd be hard-pressed to say it's beyond Twilight's potential (and probably by extension Starlight's), not to mention the possibility of friendship magic making them live longer anyway.
As for Spike, he struck gold by being born a dragon, so he's seemingly a given for being around a long time, aside from the unlikely event of an unnatural death.
Not really the only way. If Star Swirl the Bearded survives the finale (guessing he will), he can very likely cast age spells (I think it's pretty much explicit canon that he can), and I think you'd be hard-pressed to say it's beyond Twilight's potential (and probably by extension Starlight's), not to mention the possibility of friendship magic making them live longer anyway.
As for Spike, he struck gold by being born a dragon, so he's seemingly a given for being around a long time, aside from the unlikely event of an unnatural death.