Ideas for 70th birthday party invitations should be centered around whatever birthday theme you have chosen to use.

If you are using the one centered around memories, you can use an antique-white invitation found at any party supply store.  Inside, invite guests to take a walk down memory lane with all the other pertinent information for attending the party.   For an added touch, you can include a picture of the guest of honor from when they were younger and a current picture.  Of course, these can be copies of pictures.

For the Monte Carlo Night birthday theme, you can make the invitations look like a passport with Monte Carlo being the destination.  You can also use the ones that have a gambling motif found at your local party supply store, just make sure to tell the guests that they will be attending a Monte Carlo Night birthday party.  For an added touch, youc an include a few poker chips with the invitation.

If you are choosing to use the ideas for a theme centered around being beautiful inside and out, you can use invitations that are baby colors such as blue or pink.  You can include a baby picture of the guest of honor, if one is available.  If not, just attach the invitation to a mirror that says, you must have been a beautiful baby.  Invite each guest to bring along pictures of them when they were a baby so they can join in the activities at this 70th birthday party.