The risk for downs syndrome isnt based entirely on age as many people think, i think getting one for 'peace of mind' is fine, not trying to scare anyone but just remember even if your odds are 'low risk' there is still a chance of having a baby with chromosomal problems.
also, one type of down syndrome IS hereditary (there are 3 types) but it is the rarest form of ds
im only aware of this because my mum works for the down syndrome association and my brother has down syndrome so have been brought up with all the facts and fiction