I dunno I have the polar opposite of adhd which is obsessive tendencies.
Then again, someone like me who is capable of longer attention span has the following "features"
1) I practice prayer / meditation on a regular basis. You don't need to sit in a still lotus position you can meditate while walking or jogging which I find easier especially when the weather outside is below 0 Celsius. Guess the cold shocks you into instant presence / mindfulness? I remember reading about Russian monks somewhere that bathing in ice water is something they do regularly.
2) I hate watching mainstream TV. Especially the ads that seem to keep constantly changing. A cut in less than a second even if it's not about advertising some action packed fast paced movie. A BANK advertisement for crying out loud.
3) I talk slowly. I find many people talk too fast especially in the northern part of USA, and Canada. As if they're too in a hurry to get to the next point and not focused on what theyre currently saying. But in the south, I find them easier to understand.
4) I drive at the speed limit or slightly over. Never got a speeding ticket in 20 years of driving. Driving is meditative for me. I don't brake too quickly. I ease off the gas and let the car glide and gradually lose speed. Even a mechanic can't believe how long my brakes last. No weaving and constant lane changes. I drive a car like I'm driving a truck (had a CDL at some point).
That's the best I can suggest to help lengthen attention span. Hope this helps.