It's never too late for someone to quit smoking. Their health will improve after quitting, whatever their age and how long they've smoked for.
Most smokers are aware of the risks of smoking, but if you need to talk about the long-term risks, such as cancer, lung or heart disease, strokes, or diabetes you can find more information here:
Cancer
How does smoking cause cancer? (Cancer Research UK)
Lung diseases
Why is smoking bad for you? The effects of smoking (Asthma + Lung UK)
Cardio vascular disease
Smoking (British Heart Foundation)
Other health risks
What are the health risks of smoking? (NHS)
Vascular dementia
All you need to know about smoking and dementia (Alzheimer's Research UK)
Chemicals in cigarettes
What chemicals are in a cigarette? What does smoking do to your body? (Cancer Research UK)
Diabetes
Smoking and Diabetes (ASH)
Smoking while pregnant
Stop smoking in pregnancy (NHS)