What you remember reading is correct. Scars don't generally stretch or grow with the body, however there are occasions when this can occur for a while.
Stretched, or widened, scars occur when healing wounds are exposed to mechanical stress. They can be the result of the wound physically coming apart - dehiscence - and then healing by secondary intention, or from the early scar deforming in response to the extrinsic forces. Most stretching occurs in the first three months after surgery but the process can continue for up to a year.
There is no age, gender or racial predisposition. However, a stretched scar is more likely when the skin is inherently weak during repair. This can occur with collagen diseases such as Ehlers-Danlos Syndrome, progeria, and with dermal atrophy eg with advanced age or chronic sun exposure. The most significant pathogenetic factor is the inherent tension within the skin. (GP Notebook, nd).
The page also goes into how to treat stretching/stretched scars.
GP Notebook. (n.d.). Scar (Stretched). Retreived from: https://www.gpnotebook.co.uk/simplepage.cfm?ID=x20110411224140089586