doing some kind of standing warm up routine will gradually strengthen your legs as you are doing it.
this is a moderate example, but towards the end she is doing some pretty deep knee bends that i would not do at first but gradually work towards.
within a few months you should notice a difference.
after a year of doing a full Tai Chi practice with moderate depth of bending of the knees i had legs that were very strong. this was about 2 hours a week of class practice and 2 hrs a day i was practicing outside of class.
i should also say that the time i spent practicing was not the time i spent doing warm ups.

they were quite different things.
you can search youtube for chi kung, also called Qigong warm ups. all good and will give you added leg strength and more balance.