I think you can start with the dice loaded on attention span, but it is also a trainable skill. One of the biggest factors on attention is interest, finding a wider range of things interesting or finding ways view anything you encounter as interesting can help in managing attention span. Intense generalized curiosity seems to be something people are wired for in different measures and that benefits interest and attention.
Focus is an important part of intelligence and not just the measure of it. Kinda like bringing the engines online one at a time, the more focus the more processing. Also intense attention can take over the mind to the exclusion of background tasks like remembering where you just set your keys.
It seems there is a whole other type of attention span as in the type that makes people successful: Staying on task over very long periods of time like working a job and always being "on" even at home.