As others have mentioned above, you can have more than one Amex card at a time. I have 3 right now for example. I think Amex asks about previous cards so that they can look at your payment/credit history in their own records in addition to any credit check they perform. When I recently got the new Gold card (with the 2x travel points) it showed the same "Member since" date as my other cards.

And by the way, have a look at that new Amex Gold - there are a couple of threads here about it. If you spend a lot on travel (and who here doesn't) it will probably earn you more points than the Aerogold. It's also free for the first year.