If there was a tear to the muscle tissue then healing time should not be too long.
At your age, I would be more suspect of tendon tear/degenerative tendons which can take much longer to heal let alone in many cases surgery may be needed.
Aging has a negative impact on tendon health as they tend to become stiffer/reduced regenerative capacity/loss of stem cell function.
*Aged tendons exhibited structural, compositional, and biomechanical changes
Regarding tendonitis in most cases when one has been lifting weight for a long time (years) most in fact develop tendinosis as opposed to tendinitis (which they think they have) and when one develops tendinosis the tendons are much more prone to a tear as tendinosis is a degeneration of the tendons collagen from chronic overuse.
Tendinosis (degeneration) from wear/tear, aging.
As we age one needs to train smarter as you will notice it is very common for most who have weight trained for years to end up with damaged joints/tendons from the repetitive wear/tear on the body.
