No one knows. There's no age limit for treating TMJ problems, and what may happen if it's not treated depends on what the problem is, how severe it is, and many other clinical findings. Most TMJ problems are self-limited....They get better on their own without specific treatment. However, if you've had it awhile (more than six months) it may become a chronic problem. Treatment now may keep it from getting worse.
Vague. Hard to answer without a thorough history and exam. How long have you had the TMJ symptoms, what was the cause (if you know, ) the severity of the symptoms, etc. I would not wait longer to find out. See a specialist asap.
No way to know. There is a difference between symptoms resolving and underlying conditions resolving. Is it enough to be pain free, knowing the sub clinical damage continues? While there is no right or wrong, tooth damage, joint damage, muscle fatigue go on. A very personal choice, so it is important you know the risks.
TMJ/TMD is treatable. The most common musculoskeletal disorder causing orofacial pain is a temporomandibular disorder. Noises from the TMJs are a symptom of dysfunction of these joints. See an orofacial pain practitioner for diagnosis, prognosis and treatment if needed.
Depends. Most TMJ problems with "burn out" over time. So If you're not troubled by your symptoms, not getting treatment will not cause any problems.
Usually gets worse. Joint problems usually don't correct themselves. If you have a problem it will need careful and planned diagnosis to find a stable relationship and then treatments to maintain the proven stable position. Try conservative measures first. Without treatment i expect you will find the problems will worsen.