I think any singles skater that did not achieve success by the early twenties could be considered a late bloomer. For pairs that age limit has to approach high twenties. I know that's quite arbitrary, so feel free to shift them if you wish.
Here is my list of late bloomers:
Paul Wylie (27 yrs.- Oly silver; no world medal prior to that)
Rudy Galindo (1st US title at age 26; 96 world bronze)
I would probably add Petr Barna to the list. Before his bronze at the 92 Olympics, his success was pretty limited
Maria Butyrskaya- world champ at 26; not a lot of previous success, other than making the Russian world team
Shizuka Arakawa (24 yrs.- OGM)- she is a borderline case, IMO. She won the worlds 2 years before the OGM. She is a late bloomer only when you compare her with the ladies that won the OGM before her (Sarah, Tara, Oksana)
The Protopopovs- won their first OGM at ages 32 & 35.