Buttt the bottom can't be girly (which probably means this doesn't exist ;-;)
do you still like me" dk if this is the type ur looking for but u heard it's a really good story
"Love for Sale" is an age gap I can name with a masculine bottom. Though the older one is shorter. <--- (I recommend this one the most)
If you're looking for a big size difference, "The Hounds of Sisyphus" has it. It isn't age gap and the bottom is sort of pretty? Masculine enough to know he's a guy though. it's kind of disgusting for my preference.
"Sensei ni nerawareteimasu" hits a lot of your requirements except the size difference isn't that big. Warning, the age gap is disgustingly creepy for my preference. But, since it fits I'll put in here.
That's really all I could remember. It truly is hard finding bottoms that don't look like girls in the age gap genre.
Any yaoi with age gaps where the older one is a lot taller??