You can generally join the U.S. military starting at age 17 with parental consent, and 18 on your own, with exact age ranges depending on the branch.

Basic age rules

  • Minimum enlistment age is 17 with written parental consent in every branch that accepts 17-year-olds.
  • At 18, you can enlist without parental consent.
  • Federal law caps enlistment at 42, but each branch sets a lower maximum age.

Typical age ranges by branch (active duty)

These are common current ranges; specific programs or waivers can shift things slightly over time, so recruiters have the final say.

  • Army: About 17–35 (some sources list up to 41 depending on policy updates and prior service).
  • Marine Corps: 17–28.
  • Navy: Around 17–41.
  • Air Force: Roughly 17–39 or into the early 40s depending on role and current rules.
  • Space Force: Generally 17 into the late 30s or early 40s.
  • Coast Guard: About 17–41.

Other things that matter

Even if you meet the age requirement, you still have to:

  • Pass medical and physical fitness standards.
  • Meet education rules (usually a high school diploma or GED).
  • Take and pass the ASVAB aptitude test.

Example: a 17‑year‑old

If you are 17, you can talk to a recruiter, have a parent/guardian sign consent, take the ASVAB, and—if you pass medical and other checks—swear in and ship to training after finishing the required paperwork and school timing.

TL;DR: For “what age can you join the military,” the key answer is: 17 with parental consent, 18 on your own, with upper limits that usually fall between your late 20s and early 40s depending on the branch.

Information gathered from public forums or data available on the internet and portrayed here.