Its just a visual thing, I tend to not go by measurements or by the scale
what do you mean by testosterone is the limiting factor?
Well some of this will be slightly irrelevant, so please forgive me for that..But this does, in my opinion, raise an interesting issue, in and round your concern.
Its generally accepted that Tesosterone is a major factor in building muscle.
Depending on the amounts you have, will partly decide how far you, or anyone can build.
If we then add to this basic equation, diet, rest, and a suitable training schedule, we have the basic requirements to "build" muscle.
It is generally considered extremely un likely that ladies, who use weights, to the extent a guy does, will build the same.
This is associated with Tesoserone levels.
Age, certain medical procedures, etc, will also have an affect on these levels.
Of course this is said from a natural weight training perspective. I expect we have seen lady bodybuilders who look huge. But certain people use ......how shall i say this....errrrrrr....errrmmmm...additives.

Having said that, genes should be considered as well.
Some people can just build muscle easily, some cant. And ladies can build more than they would like to sometimes.
All this is not to question your observations. If you feel that your legs are at the stage you want them, then thats cool, and congrats' on accomplishing that.

To maintain the build you have gained, try to keep to the limits you are at, in any resistance weight training, and maybe limit time spent doing these...IE, once a week, once a fortnight maybe. You might have to experiment a little, as what routine works for one person, may not work for another.
As well as keeping to your diet.
Stetching is good for elongating the leg muscles.
I think SirSunday has hit the mark.
someone motivate me...!!!!...
Could fine you 1000 virtual choc' chip cookies if you dont!
Hope you feel better SirSunday
Today:
Warm up, and stretch.
Eight sets of barbell curls, increased weight on last four sets, integrated with eight sets of standing barbell French press .. Increased weight on last four sets.
Four sets of standing overhead dumbbell extensions.
Four sets of tri-cep dumbbell kick backs.