Time cures all things ...
I remember when I was 14 counting the days until I was 18 so I could buy a rifle of my own.
Being someplace between 18 and 21 and counting the days until you can do all of those 21 year old things will pass in a flash.
Here's the law:
http://www.house.leg.state.mn.us/hrd/pubs/firearms.pdf
The Gun Control Act governs the possession of firearms
generally, the transfer of pistols and semiautomatic militarystyle
assault weapons, and the carrying of pistols. Under the
act, certain categories of individuals are prohibited from
possessing firearms. Persons who are eligible to possess a
firearm must either have a permit to purchase a pistol or
semiautomatic military-style assault weapon or must
undergo a background check before being permitted to
purchase the weapon. Additionally, persons who wish to
carry a pistol wherever they go must obtain a separate permit.
So it looks like you can do it one of two ways: With a permit, meaning that you have already been investigated, or by a notice, giving an opportunity to be investigated. In neither case does an age limit seem to be specified. That's just my casual reading though.
It looks like this is the alternative to the permit:
If a pistol or assault weapon purchaser does not have a
transferee permit at the time of sale, the federally licensed
firearms dealer may not transfer the weapon to the purchaser
immediately. Instead, the firearms dealer must submit a
transfer report to the police chief or sheriff in the area where
the purchaser resides, containing the same information
required on the transferee permit application form.
Which process is this:
624.7132 REPORT OF TRANSFER.
Subdivision 1.Required information.Except as provided in this section and section 624.7131, every person who agrees to transfer a pistol or semiautomatic military-style assault weapon shall report the following information in writing to the chief of police of the organized full-time police department of the municipality where the proposed transferee resides or to the appropriate county sheriff if there is no such local chief of police:
(1) the name, residence, telephone number, and driver's license number or nonqualification certificate number, if any, of the proposed transferee;
(2) the sex, date of birth, height, weight, and color of eyes, and distinguishing physical characteristics, if any, of the proposed transferee;
(3) a statement that the proposed transferee authorizes the release to the local police authority of commitment information about the proposed transferee maintained by the commissioner of human services, to the extent that the information relates to the proposed transferee's eligibility to possess a pistol or semiautomatic military-style assault weapon under section 624.713, subdivision 1;
(4) a statement by the proposed transferee that the transferee is not prohibited by section 624.713 from possessing a pistol or semiautomatic military-style assault weapon; and
(5) the address of the place of business of the transferor.
The report shall be signed and dated by the transferor and the proposed transferee. The report shall be delivered by the transferor to the chief of police or sheriff no later than three days after the date of the agreement to transfer, excluding weekends and legal holidays. The statement under clause (3) must comply with any applicable requirements of Code of Federal Regulations, title 42, sections 2.31 to 2.35, with respect to consent to disclosure of alcohol or drug abuse patient records.
Subd. 2.Investigation.Upon receipt of a transfer report, the chief of police or sheriff shall check criminal histories, records and warrant information relating to the proposed transferee through the Minnesota Crime Information System, the national criminal record repository, and the National Instant Criminal Background Check System. The chief of police or sheriff shall also make a reasonable effort to check other available state and local record-keeping systems. The chief of police or sheriff shall obtain commitment information from the commissioner of human services as provided in section 245.041.
Subd. 3.Notification.The chief of police or sheriff shall notify the transferor and proposed transferee in writing as soon as possible if the chief or sheriff determines that the proposed transferee is prohibited by section 624.713 from possessing a pistol or semiautomatic military-style assault weapon. The notification to the transferee shall specify the grounds for the disqualification of the proposed transferee and shall set forth in detail the transferee's right of appeal under subdivision 13.
Subd. 4.Delivery.Except as otherwise provided in subdivision 7 or 8, no person shall deliver a pistol or semiautomatic military-style assault weapon to a proposed transferee until five business days after the date the agreement to transfer is delivered to a chief of police or sheriff in accordance with subdivision 1 unless the chief of police or sheriff waives all or a portion of the seven-day waiting period. The chief of police or sheriff may waive all or a portion of the five business day waiting period in writing if the chief of police or sheriff finds that the transferee requires access to a pistol or semiautomatic military-style assault weapon because of a threat to the life of the transferee or of any member of the household of the transferee.
No person shall deliver a pistol or semiautomatic military-style assault weapon to a proposed transferee after receiving a written notification that the chief of police or sheriff has determined that the proposed transferee is prohibited by section 624.713 from possessing a pistol or semiautomatic military-style assault weapon.
If the transferor makes a report of transfer and receives no written notification of disqualification of the proposed transferee within five business days after delivery of the agreement to transfer, the pistol or semiautomatic military-style assault weapon may be delivered to the transferee.
You ARE legal at 18:
Eligibility to Possess a Firearm:With certain limited exceptions, the following individuals are not eligible to possess a firearm: persons under the age of 18 (this prohibition is limited to pistols and semiautomatic military-style assault weapons);
This means that you can buy handguns in a private sale (Federal law prohibits FFL purchases by persons under 21), and it looks like there's no reason you cannot buy any sort of rifle from a dealer as long as you comply with either the permit or the investigation.
Just a basic note: AR-15 receivers that have never been assembled to fire are neither a pistol, or a rifle. They can be built into either, and as such they are sold as if they are a pistol from an age-requirement standpoint and permit requirement standpoint. You cannot buy a handgun (or an unbuilt AR-15 lower) from a FFL until you are 21. If you want to play with AR-15's, advice is to buy a rifle and work from there.
Probably makes sense to just walk into a local gun store and have a chat with the owner. They deal with local requirements daily, and I cannot imagine anyone not wanting to help someone who wants to be a part of the sport. Smile, walk in, direct eye contact, firm handshake, and "Sir, might I trouble you for a few minutes of your time to help me understand xxx" goes a long way.
Best,
Willie
.