Should I sealcoat new (few months) asphalt before winter?
In my experience, new asphalt in a residential application doesn't begin to show surface degradation for at least a few years. By that time, a coat that you apply now will need to be redone anyway. 

I'd wait two years. If it still looks brand new, wait two more. There's something to be said for preventative care, but only if it actually extends the life of the product.