The TaxCaster tool is current. It asks for your age at the end of 2018, and will later ask for your taxable income and income taxes withheld from tax year 2018. You wouldn't have those figures available unless you've already completed your 2018 tax return.
So just continue through the tool as is. It has been updated.
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***