Bands usually begin taking off in their very early 20's. At this point they may just be beyond their first experiences with pot or even LSD. The partying is still kept to after shows and may happen only every few days. At this point they're full of unrealized ambitions and are very focused on "making it." They're an opening act and still only getting half-page interviews in magazines, but as they blow the older headliners out of the water the buzz begins †.

As their star begins to shine, people want to enter their inner circle and become their "friends." They do this by offering cocaine, Ecstasy, crystal meth, Oxy Contin, what have you. This way they become fixtures in the entourage. Different choices of chemicals result in different moods among band members which can cause friction ††, but it's overcome by their young and hungry momentum.

Their career peaks with the fourth album, and their ability to buy more of the drugs that they have become increasingly fixated on skyrockets. It would seem their success could never abate, and so they begin taking longer breaks from touring and records as they spend more time on their new "hobby".

The fifth record sells well or even better than the fourth due to the momentum, but by the sixth the sales begin slumping , and by the seventh they're debuting in the Nice Price bin . Some of the original members have left either because they're living in a flophouse or because they can't stand the chaos that the drugs and money have brought about. It's time to take corrective action†††.

The band members enter and exit rehab, and at the same time they pass their 30th birthdays. They're no longer dreaming, idealistic teenagers, they're men with wives, houses, cars and financial obligations to think about. This increases the pressure to replicate past success. This may be made additionally difficult by the fact that in just a few years the musical climate may have shifted out from under them and maybe they're not considered so hip anymore. Even though it's their job, riffing around in a garage for hours on end like 16-year-olds feels weird at 32. Most of all, they may have already blown their bucket of ideas.

All of this is reflected in the chart above. As you can see, as time passes factors like inspiration and youth decline while drug use and age increase. So I think it's more than one factor that causes musicians to produce their best music before 30. Bananas and grapefruits aren't on drugs, but for some reason they're sweeter when they're young.

† Groupie Pamela DesBarres said Jimmy Page only drank an occasional glass of wine around the time of Led Zeppelin I and II. By the fourth album it is well-known he was a heroin addict.

†† In the book Before I Get Old it is said that Roger Daltrey was an outcast in the Who in the early days because he was the only one not using speed. In The Making of Pump Tom Hamilton of Aerosmith said that often "emotions were arising out of hangovers, and that's not the normal way for an emotion to arise."

††† This is pretty much the well-known post-Rocks Aerosmith story.