Are you referring to Rankins (25) or Cam (31) ? Rankins is only 25 years old, so definitely not old .. but you are right a common disturbing trend in his young career has been serious lower body injuries.
2016 - Rookie year missed the first 7 games with a Broken Fibula suffered in pre-season
2018 - Suffered a Torn-Achilles in the Divisional round playoffs after a career regular season
2019 - Undisclosed Ankle Injury suffered in Week 14 ended season on Injured Reserve
I am concerned about his future going forward with the team this is his 5th year option season so he will become an Unrestricted Free agent after this year, so it is crucial for him to have a bounce back season for him to shed the injury-prone label and come into a nice Second contract.
On a sidenote I always thought he was carrying around too much weight for his frame; just by look you would think he has the body type of a Linebacker, or Big Safety but just bulked up to 300 lbs. which may be why he keeps having leg/foot injuries. (I don't know I could be completely off base here and maybe he's just really un-lucky so far)