Anyway, I wonder if this "Old Mare Theme" would work with other members of the Mane6?
Maybe:

Rainbow Dash gave her life to the Wonderbolts.
She spent her youth and young adulthood training to join them, then pushed herself harder once she was in.
As all of her friends settled down and drifted apart, still close, but more busy than ever with their own lives and families, Rainbow had even more time to put towards her career.
Taking over as captain once Spitfire retired, Rainbow became an icon of excellence for all pegasi to aspire towards.
Then, as her youth faded, and her speed and reflexes slowed, it happened.
It'd been brought up from time to time, but she always laughed it off.
She was as old as Spitfire was when she retired, but Rainbow was still strong.
Five years too many, it would seem, as she crashed during a show, and this time, she didn't spring back.
Her right wing damaged too much to allow for the high-flying acrobatics of her youth, Rainbow Dash was forced to retire.
And now she was alone.
Her friends visited and wished her well, but it's not like they had the time to hangout with her all day as they used too.
She had a pension and plenty of bits saved up to live off of, but no hobbies beyond reading to occupy her time, and even that lost a lot of appeal since Daring Do stopped coming out with books, the adventurous mare retiring to a college professor job and hanging up the pith helmet for good.
She couldn't work a weather team anymore with her bad wing, so she had little to occupy her time.
Moving into a house on ground-level until her wing healed more distracted her for a while, but soon she was left idle.
She realized then just how empty her life was without the Wonderbolts.
Before she could sink too far into this depressive thought, a man showed up at her door.
Her new physical therapist and masseuse meant to help her recover as best as her aged body could manage.
Anon was a strange fellow, but nice.
And those hands felt great rubbing her sore muscles, too.
But... did they linger a bit too much on her flank?
Surely not.
A young, strapping male like him with a good paying job wouldn't be interested in some washed-up has-been.
... Right?
old_dash.jpg
Artist might be https://twitter.com/rirurirue