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Based on what you have mentioned you are most likely using the Birth Date picker widget. What I would suggest is to change the available dates. You can do that by editing the form and then clicking on the same field.
Once you do, you will see the options to change this in the toolbar, so just click on Year To option.
That will allow you to move it to 2017, 2018, etc.
Do let us know how it goes or if you have any questions / issues and we would be happy to assist with the same.