Chorographer with a few minor acting roles, like in Mother, Jugs & Speed.
That’s her with the shotgun.
As seen in an old New York Daily News ad poking fun at the New York Times sports section’s often-overblown style:
Countless athletes have striven after that proverbial cup of coffee. But this season, only one will obtain the demitasse.
Ok, but when “Mickey” came out, how many people were going “oh yeah, that’s the woman who choreographed that movie”?
Likely nobody outside of the entertainment industry. 
Was this exactly Hughie Lewis and The News’ backstory?
Not a band, but rather a solo artist; and he Made It (fairly) Big (but maybe not in the US): Seasick Steve. So far as I’m aware he scuffed around achieving not much for most of his career:
In about 1969, he toured clubs in the region as a backing musician with Lightnin’ Hopkins. In 1970, as Steve Leach, he became the bass player in an innovative band, Shanti, who performed a fusion of Indian and rock music. Other band members included Zakir Hussain and Aashish Khan, and all the band members were adherents of Transcendental Meditation. In liner notes for a 2015 reissue of Shanti’s only album, writer Richie Unterberger states that “bassist Steve Leach has reinvented himself as the blues musician Seasick Steve”, and his participation in Shanti was confirmed by Seattle band the Tremens.
He left California in 1972 and moved to Paris, France, where he busked in the Métro. He occasionally returned to California where he married Victoria Johnson in 1974; they had two sons together but later divorced. Wold also spent time in the 1970s in Hawaii, and worked as a session musician and studio engineer, as well as in occasional manual jobs….
…etc
In 2006, for who knows what reason, he was booked on Jools Holland’s Hootenanny (a national institution on New Year’s Eve in the UK) and became an overnight success at around the age of 55. He now enjoys something approaching National Treasure (Overseas Division) status.
j
I remember seeing Seasick Steve on Top Gear, as one of the celebrities on the Star in a Reasonably Priced Car segment and at the time wondering who the heck is that.
Also the late great Roberta Flack, who didn’t score a big hit until she was 35. She started out her working life as a teacher, with music being more of a hobby.
Might be stretching it a bit, but how about The National? Pretty sure they met and played some in college, but think they were at least pushing 30 when they formed as The National, and did not get big(gish) until some time after that.
Actor David Soul was 33 when he had a #1 hit in five different countries, after a decade of not charting anywhere.
Ha. Not a whiff of success among that crew. I appreciate their older age, but this really doesn’t fit the bill.
The guys kicked around in the 70s for a bit, but it appears they had a pretty linear trajectory toward fame.
Rest in peace. She died yesterday I looked her up to check out her back story and found out.
The irony here is that a great example of my dad band question turns out to be a lady.
Guided by Voices were basically unknown except amongst their friends amd didnt play outside of Ohio for the first 10 years of the band. They were in their 30s with kids and had normal jobs when they got ‘big’.
Here’s another one you’ve never heard of but… she did have a number one hit in the UK, so I guess she kinda qualifies: Hilda Woodward. Another Mom Band - literally.
Woodward was born in Coventry, Warwickshire in 1913. She was raised in the former Canal Tavern pub, at the Coventry Canal Basin. During the 1960s, Woodward worked as a shorthand typist at Jaguar and performed in the evenings as the resident pianist at the Stoke Ex-Servicemen’s Club. She also played on occasion with the Guildhall Operatic Society. Woodward then married, had children and worked as a music teacher in Coventry.
Woodward’s son Rob Woodward managed and fronted the band Lieutenant Pigeon, also playing the piano, guitar, tin whistle, and providing vocals. Other members were Nigel Fletcher on drums and Steven Johnson on bass. Woodward allowed the band to use her living room for rehearsals and as a recording studio, and was recruited to play piano and keyboard for the band.
All we need now is a number one hit, right?
(Plus another minor hit the following year, so not, strictly, a one hit wonder)
j
Could her story possibly be just a little bit more British? This is an interesting example. Also Guided By Voices and Seasick Steve both seem to really fit the bill.
The closest I can come is (as always in my posts) The Cars. Ric Ocasek was 34 years old when their first album was released and he had three children at the time. One was a teen (14 YO), so that pretty much meets the trope of “teen’s dad who becomes a genuine big rock star” that was implied by the OP.
To the OP…here you go: The Middle Aged Dad Jam Band!
Yes, I know that a B-list comedic actor slumming it on YouTube with a hobby / vanity band project does not count as ‘making it big’, but I couldn’t resist. And hey, they ain’t too bad!
Several Winners and runner ups on The Voice were middle-aged and spent decades playing bars and struggling between day jobs and performing gigs.
I found several lists of Winners but it didn’t include their age.
There is a bias against older singers on The Voice. The coaches have said they prefer an inexperienced singer that can be mentored. Someone who played clubs for 20 plus years has a set way of performing.
That comes into play during the battles. When the experienced singer was obviously more polished. The coach saves the inexperienced singer.
Susan Boyle meets all the OP-s requirements.
Middle aged , frumpy and openly dismissed by the judges. Until she started singing. She sang at home and the local pub for years.
Susan toured and had high record sales.
Sadly she couldn’t handle the public attention and stress. Susan withdrew from performing after two or three years