You are 21 and got a m16 that cost about $15000-$20000. Lucky bastard.

+1 on what he said... I'm only 25 and still saving up for my first FA.

Anywho, I went with a trust as well, and I can't recall it having my DOB on it anywhere. The only place that asks it is on the back of the F4. If you read the instructions, it says "the transferee shall give full details on a separate sheet for all "YES" answers". Since the actual transferee is a trust, and not a person with a DOB, I'm wondering if this section applies to the trust, or to the trustee who is accepting transfer in the name of the trust. This may be a question for your attorney who drafted your trust.

It seems that you have three options:

1. Answer "no" since the trust is the transferee and you're acting as an agent of the trust. (I would read back through the language of your trust to see if it has any verbiage about trustees under 21.
2. Answer "yes" and provide a separate sheet saying that you are under 21 at the time of signing the form, but by the time of approval, you will be over 21 years old (probably best to provide supporting documentation of your age).
3. Appoint someone over the age of 21 as another trustee with an amendment, answer "no" to the under 21 question on the F4, have them sign the F4 as a trustee, and submit the Amendment to your trust along with the documentation to the ATF. When the form comes back approved, you will be over 21 and fill out the 4473 as a trustee and everything is good to go.

Personally I like option #3, as it is the most cut-and-dry, but your methods may vary. Standard disclaimer: I am not a lawyer, but the one who drafted my trust knows his stuff.

The other guns were form 3'd to my dealer and sold prior to applying for the form 4

Why? Is the NFA item transferred as "other" on the 4473?

Since the trust owns the weapon, as long as you are a trustee, or in this case, the grantor, you have full rights to possess the weapon. If it ever came down to it, you have the trust paperwork saying that you're the person who formed the trust, and the person who signed the F4 was a trustee at the time of signing. You could always write a second amendment to the trust removing the person who signed the F4 as being a trustee once you turn 21. Usually, people have their last name somewhere in the trust title. If police ask for your paperwork and see that the owner is "XXXX Revocable Trust" and your last name is XXXX, they will usually put two and two together.

If you were going to move, you would fill out the 5320.20 form and submit it in duplicate to the ATF. If you were wanting to take the M16 with you and leave a suppressor with another trustee, you would just submit the 5320.20 for the M16. I currently have 7 NFA items, but when I travel to Florida this fall, I will only be taking 4 of them with me. So, I just filled out the form with those four items, and I'll be leaving the other three in Ohio. Regardless of whether or not you move, the M16 will always be property of the trust, until you transfer it to someone else via a F4. Just make sure that when you leave your suppressor it is either A.) left with another trustee (also a good idea to leave a copy of the certification of trust and copy of F4) or B.) Stored in such a way that only you, or another trustee, can physically access the item.

Out of curiosity, who did you go through to get your trust done?