Help! I need to populate data based on single cell input

ok so... I have a worksheet that I am trying to get to auto populate... I tried formulas and I am sure I need code for this. I am new to code so please let me know if anyone has an awnser, code, and how to impliment it in the sheet...

basically... if D17 is equal to or greater than 18 then, B31=B7,G31=G7, B33=B9, E33=E9, G33=G9, I33=I9, B35=B11, E35=E11, H35=H11, B37=B13, G37=G13, B38=B14, E38=E14, H38=H14, B39=D15, F39=B17, I39=B18. If it is less than 18 then leave B31, G31, B33, E33, G33, I33, B35, E35, H35, B37, G37, B38, E38, H38, B39, F39, I39 blank for new data to be populated.

I was given this code: but I get an error - on the line "If Intersect(Target, Range("D17")) Then"

- the error states

Run-time error '91':
object variable or with variable not set


Private Sub Worksheet_Change(ByVal Target As Range)
Application.EnableEvents = False

If Intersect(Target, Range("D17")) Then
If Range("D17") >= 18 Then
Range("B31").Formula = "=B7"
Range("G31").Formula = "=G7"

'OR IF YOU WANT VALUES INSTEAD

'Range("B31").Value = Range("B7").Value
'Range("G31").Value = Range("G7").Value
End If

Else
Range("B31").Clear
Range("G31").Clear

End If

Application.EnableEvents = True

End Sub


Can anyone help?

Sure, this is only the first step of what I need done... I have attached the spreadsheet, basically I need to not replicate the data if I dont need to

so if the patient is over 18, then the legal guardian info should be the same as the patient, I cant leave it blank, but I dont want to enter the data twicetest book 1.xlsm

I hope it attached correctly...

secondly is the policy holder, if it is yes then the patient info should be the same and copy over

this will be the template, I want the users to only be able to enter data into the highlighted cells, if the patient is 18 or over then the guardian info will be the same. if the patient is the polich holder then again the patient info is the same, ditto on the secondary ins carrier.. and so on, I just cant figure it out.. thanks for your help.. once the patient info is entered then the form will be saved under the patient name, and a new blank template will be opened for the next patient