The number of young heroin addicts has dropped to its lowest recorded level.
Some 4,268 adults aged 18 to 24 started treatment for heroin addiction in 2011/12 for the first time, a fall of nearly two-thirds from 11,309 in 2005/06, figures from the National Treatment Agency for Substance Misuse (NTA) showed.
But the over-40s now make up almost a third of the whole treatment population, with more than 16,000 starting a new course of treatment last year.
Heroin also remains the biggest problem for drug addicts, with four in five of the 197,110 adults in treatment in England being treated for heroin dependency or for heroin and crack.
Paul Hayes, the NTA's chief executive, said: "Treatment needs to accelerate its recovery focus if more of the ageing heroin population are to successfully complete treatment and get their lives back on track.
"We should be mindful that economic problems have historically exacerbated drug addiction."
Mr Hayes also said there was was a "savvier generation of young people who seem to know what heroin and crack are going to do to you".
"The original pool of heroin and crack addicts is shrinking," he said. "And because fewer people are using heroin or crack, it's not being topped up.
"Less positively, there's an increasing challenge from older drug users, many of whom are still in the system and others who began using in the 80s and 90s are now beginning to access treatment as their health deteriorates.
"These people became addicted to heroin during the epidemics of the 80s and 90s. Some are trying treatment for the first time this year, others have tried treatment, relapsed and then come back in, or have entrenched use that presents a significant issue for treatment services, not least because of the sheer numbers in treatment who are aged over 40."