There are really too many variables involved to say with certainty what a scar will look like after x number of years. As a rule, scars are pretty vascular in the short term - up to a year or three. They generally fade and flatten out over time, becoming less noticeable, but if they are in an area of tension they can stretch since they are less elastic than normal skin.
The style of wound closure can influence the final look of a scar. Sutures can be of the dissolving or non-dissolving type; in general the nondissolving type is stronger and smoother for a given diameter, so a thinner suture can be used with less inflammatory response to the presence of the suture. If nonabsorbable sutures, or staples for that matter, are left in for an extended period, you get that classic cartoon crosshatched scar effect from reaction at the spots where the suture enters the skin. Absorbable suture is placed below the surface and doesn’t give you that crosshatched look.
Infected wounds don’t heal as quickly or prettily as clean wounds. Lacerations (crushing/tearing) don’t look as pretty as incisions (cutting). Nutritional status and overall health of the patient plays a role. Some ethnic groups are more likely to form keloids than others. Some people just have PPP (“piss poor protoplasm”, a term of art) and can’t heal for shit. Mature scars can end up with more pigment, less pigment, or the same amount of pigment as the surrounding skin.
Lacerations seen in the ED are usually handled by the ED physicians unless they feel that there is some extenuating circumstance. A plastic surgeon may get paged on a case-by-case basis: more likely if the patient is a child, or female, or if the laceration crosses the ear or margin of the lip or eyelid. Contaminated wounds may just get pulled together with butterfly tapes or a few widely placed sutures to allow for drainage.
Let’s take as an example a scar on my wife’s cheek/chin from the removal of a skin cancer. She had a MOHS procedure, so a fairly good sized chunk of skin was removed, with the final wound getting shaped into a pointy ellipse. A dermatologist did the wound closure by raising skin flaps at the edges and closing the wound under some moderate tension with an absorbable, buried suture. The upper and lower parts of the wound healed quickly, but she got a small stitch abscess at the site of the suture knot, where the tension was at maximum. That part of the wound healed with a broadened scar that remained pink and raised for more than a year after the rest of the scar had faded. Now (4yrs later) the whole scar is flat and pale, but still wider in the middle. I think that a plastic surgeon would have taken more time to shape the wound, maybe doing a z-plasty to change the orientation and reduce tension. A fine nonabsorbable suture, removed as soon as possible, would have helped too. She could have had treatment with silicone pads to promote flattening of the scar afterward.
So, in the final analysis: you might be able to look at a scar and say that it was pretty new (<5 years, say) because it is still kinda raised and vascular (pink or purplish, blanches to finger pressure) or old (>2 years, say) because it is flat and ‘pale’. Note that there is a lot of overlap there. I wouldn’t be able to say whether a mature scar is 10 or 15 or 20 years old.
