Guys want to lower it because they like younger girls. The truth is that men cannot understand women anymore than we can understand them. At age 18 most girls have had no life experience or hardly any with men which makes them easily manipulated. 21 is perfectly acceptable and you cannot compare warfare with prostitution. There are plenty of 21 year plus girls to work in this business. There is not shortage.
Also I can see where having your girls young means you can keep them under the LPIN "rules" easier. They are less likely to speak up and do anything.
In other words, as you say, it's a crock of shit.
The weird justifications people try to use is bullshit as far as the eye can see.
In most states (if not all) you can get your drivers license at 16. Is 16 old enough to be sent to Syria with an assault rifle? Is 16 old enough to be handed smokes and booze? Is 16 old enough to own or rent property? Take out a credit card? Work with heavy machinery? Work a job that requires access to sensitive information? I say no. I know way, way too many immature 16 year olds. Hell, really, 16 isn't mature enough to operate car farther than short distances (with exceptions being they have working papers and need to get to a full time job, or their family works a farm or livestock ranch then supervised they should be able to help out). You know what 16 year olds do? Smuggle cigarettes and wine coolers. Get drunk, smoke, and try to light things on fire. Have unprotected sex in the back of a movie theater and think it's funny. Make accounts on Wikipedia to edit serious articles to make all important historical figures gay. Praise their love to 5 Seconds of Summer all over the internet. That's what 16 year olds do. You think they're really old ad mature enough to make decisions that could easily impact the rest of their life, let alone potentially the life of another person? Hell no. The "16 and Pregnant" and "Teen Mom" TV shows are spectacles for a reason. Because almost always the stories on them are absolute trainwrecks.
I was a complete twat at 16. I thought I was mature and knew everything and how to handle myself. In hindsight - fuck no. I knew jack shit. Thank my lucky stars I was in a same sex relationship at the time or I could've been on Teen Mom. Oh hell no. More than half my friends were 19-22. I got snuck into college parties all the time. If it weren't for some older friends who had my back boldly warning people not to touch me because they could get their asses hauled to jail I could've been date raped in an instant. When you're in high school you tend to find it flattering when older people think you're mature and attractive, but hindsight is 20/20 and looking back the older guys who salivated at a 16 year old? Disgusting. Go for someone your own age and if you're having no luck then
you need to grow up. Not
prey on younger people. 18 is not much different at 16. Not in body structure. Not in maturity levels. Not in life experience.
Hell, I disagree with the cultural expectation that people must start college and know their career path at 18. That to be undecided until halfway through college, or longer, is wrong. Countless people regret their choice of career paths when they started college. And studies are showing that the timing has something to do with it. It isn't until at least 23/24 that human beings have a better grip on who they are and what their strengths and weaknesses are, especially in the modern first world. 21 is seriously the bare minimum age a human being, especially a human being in a modern society like we have in the US, has had enough life experience and physical, emotional, and mental maturity to make executive decisions - to understand the consequences to things. And yes, the choice to go into sex work has consequences.
If you like younger women there are plenty of them who are 21 and older who
look much younger. Makeup goes a long way (and there's plenty who don't need makeup to look great). Body tightness stays well past a woman has hit menopause. A woman in her 40s whether she had kids or not can be just as tight as a woman in her early 20s. And if you're paying for sexual services you really should be looking for a sex worker who has experience and knows what they're doing so you get your money's worth in pleasure. An 18 year old may look cute but she might also bite your dick when going down on you for a BJ. Or not understand only one movement does not make for the best manual stimulation. When you're getting your expensive car worked on do you want the kid who is barely through their training to handle it or the mechanic who has had several years' experience with cars? The choice should be obvious. You should want your money's worth. 18 year olds interested in adult work should start slow learning the works of the industry by doing cam work, clips for sale, experimenting with consensual partners their age, so they can figure things out - then when they have enough experience delve deeper into the business if they so choose.
Coercion and manipulation is not proper consent. Don't opt to screw up adolescents before they even had a chance to gain life experience to figure out who they are and what they really want in life.