My youngest had it when he was 4! I think it is neat! A creative outlet.
They surely are creative with them. The sets might get assembled in intended fashion once and then they soon get reassembled as ships and all sorts of other crazy stuff. Both are more mechanically inclined than either of their parents. I think that inclination skipped a generation.
Try not to vacum up too many.....lol.
Too late!

Luckily we have a vac that makes it easy to look for something if you know you sucked it up.
I hate to think of the amount of money my wife and I spent buying Lego sets for him that wound up strewn all over and never able to be re-assembled
We have container after container of Legos. We aren't the only ones who buy them though. Every birthday and Christmas they sucker grandparents and friends into getting them for them. They drool over Lego catalogs the way my dad does with gun and car digests.
my son is obsessed with video games
We let the boys go at the Legos all they want but seriously limit the video game time.
I see nothing wrong with a Legos obsession at 7! Or any other age! ;~D
Could be much worse obsessions for sure.