From information I read it seems all new moles that appear could be cancerous. whats the truth?

I think you can develop new moles at any time. what you are looking for is changes in them over time. Look out for a halo around it, itchiness, bleeding, irregular shape, if it grows wider than half a cm. If you get anything like this it MAY be a melanoma but if caught early its easy to treat. I have had a couple of moles taken off over the last few years at the early stage of changes. And one final piece of advice give up the sunbeds now and invest in a good fake tan. It really isn't worth the risk.