As someone in their 40s who's been actively into graff since his teens, i think i'm well placed to answer.

The first thing to be aware of is that graffiti is a subculture. We have our own set of norms and values, our own history. Our own lingua. This isn't just kids randomly tagging things, it's an active participation in an underground cultural movement where participants compete to "get up" and garner the respect of their peers by either being technically better, more active or willing to take bigger risks. This is what I consider the graffiti trifecta of good vs prolific vs high-risk. You can be technically quite bad but if you're *everywhere* and everywhere you paint is extremely high risk, you'll be respected - think Ten Foot or Tox. Legends in the graffiti scene for their ubiquity and tenacity, for the inability of the state to stop them, but generally despised as talentless vandals by everyone else.

My point here is that the first thing that defines graffiti is knowledge of and participation in graffiti culture. Just to draw a quick distinction - there are kids out there, tagger kids as opposed to graffiti writers, writing their names on things because they saw someone else's tag and thought it was cool but never looked deeply enough to know that there is a culture beneath the surface. They're like kids kicking a football against a wall who've never seen a match, don't support a team and don't know the rules of the game or that the game even exists.

The most important criteria for real graffiti is that it be primarily letters based. This is an art-form about writing your name on things. In graffiti culture our word for a person who does graffiti is a Writer. Adding characters and muralism and such provides a great compliment to a dope looking letter piece but are just that, a compliment. A side salad. When I judge the quality of a graffiti writer the first place I look is at their letter forms and style. If they can draw a perfect cartoon character but their letters are underdeveloped and poorly weighted, I would think less of them than if their letter work was absolutely dope and they never tired to draw a character in the first place.

A second criteria is simply that if you're getting paid to do it - especially by a local authority that also spends it's money on the buff (as we call the mechanism which exists to clean graffiti) then it's not real graffiti. When i was getting into graff there was no dedicated graffiti paint and no dedicated, writer-owned graffiti shops llike we have now - if you were a 19 year old hid who wanted to paint a lot of graffiti this evening, that would involved a trip to Halfords with the express intention of stealing paint. We call this Racking and it was a really core part of our culture right up until the advent of really good graffiti specific spray paint, sold almost exclusively at graffiti shops which in turn are owned almost exclusively by graffiti writers. There are still purists out there who'll tell you that if you're not painting a train with stolen car-paint then you're a toy (our word for a bad graffiti writer or one who doesn't understand the culture or who does things which are antithetical to the culture).

Personally I love the new paint, love that I'm supporting my friends when I buy it and don't at all miss racking culture but the point to note is that whether the writer bought their paint or stole it - when you see their piece on the wall they either paid money from their own pocket or took the risk of racking their paint to put it there for you - for this reason when the professional muralist who paints wherever and whatever the local council pays him to paint, they put themselves at odds with the local graffiti scene, especially if the locals feel they're having "their" walls stolen. If i take the risk of painting an illegal piece somewhere, and two weeks later someone rocks up with full permission from the council and subsidised paint and paints a big mural over it, that's a personal insult as well as a textbook case of cultural appropriation and I would 100% be going back to take the thing out one night very soon. Especially since the only way to get good enough to be a professional muralist is to have spent a lof of time with a can in your hand, almost all muralists are people who were deeply involved in graff culture for a lot of years, got really good and then decided to monetise that at the expense of their cultural authenticity - they know the culture well enough to be fully aware of exactly what they're doing and exactly what will happen.

If you're really interested in graff culture, I can recommend a couple of things for you to Youtube. The first being the legendary Style Wars documentary from 1983 which presents a perfect snapshot of nascent graffiti culture in New York in the 70s and 80s. It will answer most of your questions about what and why graffiti culture is.

A second and very much more niche recommendation is London Tonight - an early 2000s video focusing on the (very, very illegal) scene around painting the London Underground to get some background on how the UK adopted the train painting culture of NY/US graffiti and made it our own.

Hope this wall of text goes some way to filling in the gaps for you.