A few years ago I was working a lot, hadn't been to the gym in years and so on. I decided to just do 3 gallon batches.
It was really manageable, and it slightly shortened my brew day.
I've been working out a lot over the past year and 5-6 gallon carboys seem pretty easy now, but in 10 years I can imagine switching to 3 gallons.
when im 60, maybe it'll be 1 gallon...