How likely will a 20 year old get cancer or lymphoma? don't smoke don't do anything like that or alcohol. symptoms?

Low odds: If you adopt a healthy life style like you are already doing to some degree, the risk of developing Cancer are reduced markedly. I would recommend to you, keeping a healthy weight, eat healthy foods(ample amounts of vegetables and fruits daily and avoid animal fats(meats and dairy products) and do regular exercise(preferablet 30 minutes or more daily). That will give you good odds of not having ca

Unlikely: Without any risk factors (family or environmental) and no smoking, etc, it would be unlikely for a 20 yo healthy individual to acquire cancer. Depending on the cancer in question, the symptoms would be indicative of that specific type. (for example-coughing, short of breath, blood in your sputum, etc. may be lung issues, etc.)