It is normal to get new moles up until the age of 34 to 40. Just because you notice a new mole does not mean you have skin cancer. But, it's important to pay attention to certain details.
The number one thing I tell my patients is to look for the ugly duckling. If you get a new mole that does not look anything else like the other moles you have, that's when you need to see a dermatologist to get an evaluation. It's also important to know that as you age, your moles will age. A mole that starts relatively brown and flat, as you get older, will become light brown and elevated and eventually may lose its color completely. This is normal. You need to look for the ugly duckling. If you get a new mole that does not look like anything else on your body, that is when you need to see a dermatologist.
What you also need to notice is that as we get older, we'll start getting new types of growths that are not moles. These are called seborrheic keratosis and lentigos, also known as liver spots. It can be difficult to differentiate between a seborrheic keratosis and a normal mole. Seborrheic keratosis tend to look like a sticker - stuck on, sharply demarcated, almost out of place. They oftentimes happen in sun-exposed areas, and they often look like each other. So if you notice anything that doesn't look like the rest of the moles, or keratosis that you have, you should see a dermatologist, and probably get a skin biopsy.