No. While there are many factors that may contribute to ADHD, such as genetics (heredity), environment, and diet, the mother's age at conception does not contribute to the disorder. However, a mother's age at conception (and due to the age and quality of her eggs) can contribute to other disorders and syndromes such as Downs and Klinefelter. As eggs mature and break down, there is a greater chance for chromosomal abnormalities to occur within the embryo, despite the embryo developing to term and becoming a deliverable (and often quite healthy) child.
Example, a girl of 17 has a normal, healthy child. 3 years later she gives birth to a child with ADHD. 9 years later she has another normal healthy child and 6 years after that has a child with OCD. 5 years after the birth of the last child, the woman, now in her late 30's who has had for the most part, 4 normal pregnancies and 4 relatively healthy children, now miscarries with twins who were not developing but then goes on a year later to have 2 healthy twins.
Everyone is different and working closely with doctors is the best method to track pregnancies. There are so many tests that can be done before becoming pregnant and while pregnant that can determine potential issues before the baby is delivered.

Probably. I mean it a contributing factor in that older parents have had a lifetime of being able to come and go as they please many find it an unimaginable shift in priorities to have a child need them 24/7 and they react by plopping the baby with sitters/daycare in front of a TV which can't be a good thing. Also many older parents have left interesting careers and are slightly resentful of the lifestyle full time parenting demands. That in itself would cause ADHD but it would contribute