OK ....  If you are 65 or older the 1040-SR will be used automatically  but it makes absolutely NO difference. 

This new 1040-SR is the silliest thing the IRS has done to date … what a waste of effort & paper… the new 1040-SR  is EXACTLY  the same in line information  as the 1040 this year ... the ONLY differences are  the font size, background color (that TT doesn't print)  and the fact that they added a standard exemption chart to the bottom of the first page of the SR form ...

LOOK at them side by side and have a good laugh. 

I still can’t find any reason why the form 1040 could not simply have larger font and no background color ( which used to differentiate the 1040, 1040A and 1040EZ apart from each other which is no longer needed).  Thanks goodness my  professional tax program has the sense to the new larger font on the form 1040  so we shut down the option to use the useless 1040SR form so we don’t waste ink printing the unneeded charts at the bottom of the first page.

https://www.irs.gov/pub/irs-pdf/f1040s.pdf

https://www.irs.gov/pub/irs-pdf/f1040.pdf