My screen indicates you are using TurboTax Business. This would indicate to me that you are filing a 1065 Partnership return. (Partnerships and multi-member LLC's both file the same 1065 return.) It also indicates that there is more than one owner of the business. (You can't file a 1065 with only one business owner. Period.)
Therefore your start date of the business "MUST" be the first day the first rental asset was available for rent. It does not matter if it was years ago either.
The "BUSINESS" was started in 2013.
The "PARTNERSHIP" was started in 2018.
You also have the nightmare of ensuring that prior year's depreciation is allocated correctly, as all depreciation between 2013 and 2018 up to the month you transferred the rental from your personal tax return to the partnership, is 100% allocated to you personally, since you personally claimed it on your 1040 tax return.
All depreciation after the rental was transferred to the partnership in 2018 is split between you and any other partners of the business.
I have been informed that a fair number of CPAs do not do this allocation correctly for folks dealing with your exact situation. But I make no claims as to the accuracy of what I've been "informed of" either.
