Probably, but it depends on the Child Status Protection Act calculation. His age is generally treated as frozen at the date of filing for the period the petition is pending, and a visa must be available and sought within the required time.
Run the age calculation before filing, not after
Under the Child Status Protection Act, a child's age for derivative purposes is reduced by the number of days the immigrant petition was pending, and the child must then seek to acquire permanent residence within one year of a visa becoming available. For an EB-5 investor filing while her son is 19 and a half, the protection usually holds if the petition is approved and a visa number is available without a long wait, but the arithmetic must be done with the actual filing and approval dates and the visa bulletin, and it can fail if visa availability regresses. The practical responses are to file as early as the source-of-funds file allows, to keep the son unmarried, since marriage ends derivative eligibility regardless of age, and to check the calculation with counsel at each stage. If it fails, the son needs his own route, and that plan should exist before the birthday, not after.
Hypothetical example: an investor's twenty-year-old daughter plans to marry shortly after the petition is filed. The first review should calculate her protected age using actual petition-pending days and identify the visa-availability date, while also explaining that marriage ends derivative eligibility. Receipts, approval notices and the visa bulletin settle the timing calculation. Make a family decision before the wedding date: she may need to remain unmarried until she has acquired residence or pursue a separate route. Hoping that the family's filing alone preserves every option is not a plan.