In the U S Forces, a Lance Corporal is an E-3 (but then I’ve been out of it since 1963, so a lot could’ve changed). In today’s military, it’s not uncommon for an E-3 to be a 19-year old. I was, back in the day. In my day, if a guy was a 47-year old and an E-3, it would be a rarity. I was an E-4 at a base in southern Italy and pulling KP when a new cook showed up. He also was an E-4 (three striper in the Air Force). He told me that he made his grade on Guadalcanal in 1942. I think he was about 45 at the time.
Somebody can make Lance Corporal quickly and will do so if they are considered a potential Sergeant or Warrant Officer, but it is considered advantageous to have highly experienced Privates as well, to help guide along the younger blokes.