Why was a 1040 - SR used instead of 1040 for my taxes ?

A Form 1040-SR is used if you are age 65 or older.  It is EXACTLY the same as a Form 1040 in every way except for the larger type on the form.  So, No that is not the reason you have not yet received a federal tax refund.

The dates shown on the TurboTax Tax Home webpage are Only Estimates.

Once a tax return has been Accepted by the IRS or a State, TurboTax receives no further information concerning the tax return or the status of any tax refund.  

If accepted by the IRS use the federal tax refund website to check the refund status - https://www.irs.gov/refunds
If accepted by the state use this TurboTax support FAQ to check the state tax refund status - https://ttlc.intuit.com/questions/1899433-how-do-i-track-my-state-refund

After the tax return has been Accepted by the IRS (meaning only that they received the return) it will be in the Processing mode until the tax refund has been Approved and then an Issue Date will be available on the IRS website.
See this IRS website for federal tax refund FAQ's - https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions