My child aged out due to a wrong I-526 form filed by my immigration attorney. What options do I have?

You should not be penalized for attorney error. You should have (a different attorney) assist you in filing for a nunc pro tunc since the circumstances were beyond your control in timely filing.

If I-526 was rejected due to an outdated form used and USCIS has not receipted the case, then it is not possible to use that I-526 to include your child as derivative. One option is to file a separate I-526 for your child as the principal EB-5 investor with a separate qualifying EB-5 investment. Other immigration options may be available for your child as well, such as work visas or marriage to a U.S. citizen. Consult an immigration lawyer to review options.

You should consult with an experienced immigration attorney to determine all of your options.

Re-apply with the child as the principal.

If your EB-5 investor petition filed on Form I-526 was rejected for whatever reason, including the fact that it was filed on the wrong form, it would unfortunately mean from the facts presented that your child would have aged out since you did not file an approvable EB-5 investor petition on Form I-526 until after your child was already 21. You may have few viable options for your child. One may be that Congress in future legislation would allow you to substitute your child for you as the petitioner, but that would mean you and your wife would forfeit your right to apply. You could file a new I-526 petition in the name of your 21-year-old child, but that would require an additional investment.

It is imperative that you contact new immigration counsel.

You may have to file it.

Unfortunately, the age of the child at the time of approvable I-526 is filed determines whether the child could be included. If USCIS issued a receipt notice and the second filing could be considered a supplemental or amended petition, then you may be able to argue that the first filing froze the age as the pending I-526. However, if the original, first filing was returned without being received, then you may be out of luck.