Wanna know "what dreams are made of?" Our fun photo gallery featuring Hilary Duff's hottest shots ... the millennial icon may be well into her 30s -- 38 years old today to be exact -- but based on her sexy selfies, she doesn't look a day over 21!

It's a rare sighting for the hot mama of four to flaunt her fit figure -- so mirror selfies like these are worth posting for ...

Backside booty shots in a silky smooth mini-dress?! Say less!!! The "Lizzie McGuire" star is known for bustin' out the weights during her workout regime, and all we can say is, "keep lifting Hilary, 'cuz you're lookin' booty-ful!"

And don't miss out on shots like this one -- Hilary heats up her page with hot legs and toned calves on full display while rockin' a sexy pair of boots!

Get your booties into our photo gallery ...

"Let the rain fall down, And wake my dreams, Let it wash away, My sanity, 'Cause I want to feel the thunder I wanna scream, Let the rain fall down! I'm coming clean!"

Happy Birthday, Hilary!