There was a study some time ago that found that autistics have a similar shortened lifespan of roughly 5-7 years off, although the good news is that's lower than it was 10 years ago, where it was something like 19 years shorter. There were some interesting biological pieces, including that autistics tend to develop more neurological conditions as they age, so that contributed to mortality.
However, it's important to look at quality of life when you're looking at aging. A lot of people with ADHD have a harder time holding down steady work, finding partners that support them, steady housing, and often times are dealing with a much higher level of residual stress and often maldaptive coping mechanisms. (Same is seen with autistics.) These things add up. That's why, within the autism community at least, there's a lot of interest in autistic elders, and figuring out how they have good aging. A lot of it comes down to a supportive job and home environment.
GREAT MOMENTS IN HISTORY (#7): April 2, 1751 Issac Newton becomes discouraged when he falls up a flight of stairs.