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  • Writer's picturePetra

Developmental Delay, or Being a "Late Bloomer" - Implications for ADHD Across the Life Span

An aspect of ADHD that often goes unaddressed is the concept of developmental delay, or as I more often phrase it, being a "late bloomer." This term offers a more positive and hopeful perspective on the challenges faced by many of those with ADHD, suggesting that while development in certain areas may take longer, growth and improvement are very much possible.


The Nature of Developmental Delays in ADHD

Developmental delays in ADHD refer to the slower maturation of some cognitive and social skills compared to neurotypical peers. This can manifest in various ways, such as myriad challenges with executive functioning, emotional regulation, and social interactions. Many young people with ADHD may find themselves achieving milestones in these areas at a later age than expected or when compared to same-aged peers, which can lead to feelings of frustration, inadequacy, and being out of step or left behind. This can colloquially be referred to as having problems with "adulting".


Russell Barkley's Perspective

Renowned psychologist and ADHD researcher Dr Russell Barkley has extensively studied ADHD and its impacts over his decades-long career. Barkley maintains that individuals with ADHD generally exhibit a significant delay in the development of all aspects of self-control. He often talks about a 30% delay in these areas for children to young adults, although this number is rather a rough summary of his findings rather than based on any measured variable/s.


Using this 30% delay, a 10-year-old child with ADHD might exhibit the self-control skills of typical of a 7-year-old, and an 18-year-old may be more like a 13-year-old. This gap can provide a framework for understanding a child's or teenagers' behaviour within the context of their developmental stage, rather than through the lens of intentional misbehaviour, defiance, or being "lazy". It also raises issues about when children and teenagers with ADHD should take on roles of responsibility, such as when a teenager with ADHD should be allowed to obtain a learner's driver license (Barkley says flat out no to 16), and whether it's a good idea to send an 18-year-old a different city on their own to attend university. In my own situation, it will be some time before my 8-year-old son will be allowed to walk to school on his own, and even though 14 is the minimum age for a child to be at home alone in New Zealand, that may well not be happening in my household.


So often when I talk to the parent of a person I am assessing for ADHD as an adult, there is a pattern of support being withdrawn for various activities around the time that high school starts - around age 13. At this point the child may be expected to manage their own homework, pack their own schoolbag, get to school on their own on time, or make their own lunch. These are all things that would seem to be good steps for developing independence, but I bet you can guess what happens for many kids with ADHD. Without ongoing external structure provided by a parent or caregiver, these behaviours can rapidly fall away. By understanding that many children and teenagers with ADHD operate at an age around 30% younger when it comes to self-control, it could be prudent for a parent to maintain structure for their child into and perhaps through the high school years, and perhaps even into young adulthood.


But what about adults with ADHD; are they perpetual teenagers? While the brain appears to be fully mature around the age of 30, Barkley asserts that adults with ADHD will often get to around the developmental age of a 20-year-old in terms of self-control skills, and stick there until the inevitable declines of executive functioning that occur in later life. So while the brain finally does "grow up", most people with ADHD will continue to have difficulties compared to same aged peers when it comes to issues of self control broadly defined. And when you think about it, that makes sense when you think about the 18 symptoms of ADHD, and how they must create functional impairment in order for a person to be diagnosed in the first place.


Embracing the "Late Bloomer" Concept

While developmental delay appears to provide quite a good model for challenges that people with ADHD may face, I prefer the term "late bloomer", and have heard neurodivergent people referring to this concept themselves, such as Australian comedian Hannah Gadsby, who received an ADHD and then autism diagnosis in her late 30s. Being a late bloomer acknowledges the unique timeline each individual follows in their growth and development, encouraging a focus on personal achievements and progress rather than comparisons with others. At times I tell my ADHD clients in their late teens and twenties that they have the benefit of more years of brain maturation in front of them which will hopefully in itself help with some of their persistent symptoms and difficulties.


Of course, everyone is different, and I meet people of different maturity levels at different ages. The late bloomer concept does not apply to all people with ADHD, but I have found it quite helpful as a parent of neurodivergent children to alter my expectations about what they may need from me in their childhood and adolescent years, as well as expecting that they will need more support as young adults than I did at the same age.


  • Hannah Gadsby's book Ten Steps to Nanette is an engaging memoir of a neurodivergent queer woman eventually finding her way in the world (with support), despite myriad struggles faced along the way

  • Dr Russell Barkley presents his ideas on developmental delay in part 1 and part 2 videos on his YouTube channel





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