I will explain what I believe is a twink.
A twink is a young man who is typically 18-22 and has no body hair, especially on his upper-chest. The term is normally considered gay slang.
He can be considered effeminate, though I don't personally subscribe this attribute as being necessary. In my opinion it is solely the physical appearance that makes a guy twinky.
There are two theories of the origins of the word. The first is an abbreviation: "Teenage White Not Into Kin"" but twinks can be of different races so I don't like that theory. The second comes from a chocolate bar called Twinkies which looks good on the outside but there is little of substance in the inside.
According to Oxford Dictionary the term originated in the seventies and can be a young man regarded as an object of homosexual desire.
They can have tattoos, piercings or glasses. Though I prefer them without accessories or body art.
Some shave or wax. Although some guys are naturally smooth such as asians. I don't believe that there is a way to tell if a guy is a twink if he does not go shirtless or lift up his shirt to expose his chest.
Another critical part is being clean-shaven.
Basically they are attractive because they look young and many people are into that image.
Their weight doesn't necessarily matter but they are generally considered to be skinny but not into the whole body building scene. I am sure that this point would be debatable.
Personally I like them skinny. I like abs but they look good without them too.
You can find some in colleges and gay nightclubs.
Their type of body is popular with entire porn studios dedicated to them.
They are generally considered to be gay or bisexual. Though in my personal view it is the body type not sexuality that is important but from reading online this view is not widespread.
In mainstream culture some could be considered idols or heart-throbs. Obviously if you are subscribing to the belief that they can only be gay or bisexual then there would be very few of them. Since more people feel comfortable coming out there would be more twink celebrities in comparison to the past.
The definition in Oxford Dictionary would appear to be broader than just gay guys so I don't see any reason not to include straight guys. It could be worth noting that the broad definition opens up the door to any young man being considered a twink. Obviously it can mean different things to different people.
A related body type is the jock physique. You usually see both types together in gay porn. The only real difference as I understand is a jock has a more athletic body.
Even though the age requirement is 18-22 some studios go beyond that with ages up to 26. I think that how long a twink stays in a studio would depend on how popular he is with their customers.
In the 2007 book "Never Enough" by Joe McGinniss they are described as often blond and often white. This would not appear to be accurate as they have a wide range of skin and hair colors.
You can self-identify as a twink but some people use the word as an insult just like the word bimbo is used to describe a woman that is young, pretty and dumb. I expect that the insult is just another way for older people to put-down the young to make themselves feel better.
Similarly to the "Never Enough" example a bimbo is often blond. I have never heard of bimbo porn and women don't self-identify as bimbo. This means that while the terms are similar there are some distinct differences between the two terms.
There are also different types of twinks and some of the types are feminine, Euro, and muscle. Muscle twinks would overlap with jocks I think and the main difference would be that jocks can have more body hair. Two other popular types are Asian and Latino.
Some dating sites/apps such as Grindr use the term and there are dating sites that are devoted to them but I can't speak to their legitimacy. Many twinks will probably use mainstream websites.
Like most people they usually date guys their own age but this isn't always the case.
Men that have come out later in life would be less likely have have experienced a relationship with a twink.
I am sure that if they are closeted some would have secret relationships. It is possible that the internet makes this easier.
The internet may also make coming out a bit easier as there are stories and support groups that were not accessible to previous generations.
Another type of gay guy is a pup. The main difference is pups may or not be hairy and some consider them to be more intelligent. The other main type of young gay guys is cubs and they have hair on their chest and face.
For me it is all about having a smooth body and face. They can be considered intelligent. Additionally if they work on their bodies I think that should be applauded.
A twunk is similar to a hunk or jock. He would have a body of a hunk but is young and smooth. Some claim that he's older but from what I can tell this view is not mainstream.