Do we know what age Leah and Rachel were when yakove married them?
If yes what is it? Source please.
Are there any midrashim on the subject?
The Seder Olam Rabba (ed. Leiner) states (ch. 2) that they were twins and were both 22 when they got married:
נמצאו רחל ולאה נשאו בנות כ"ב כ"ב, שהיו תאומות
Thus, Rachel and Leah were both married at age 22, for they were twins.
According to Rav Chaim Kanievsky's sefer Lamechsa Atik, which gives names and dates and other unspecified details for the Chumash, the Vilna Gaon's version of Seder Olam Rabbah has it that they were both 21.
Seder Olam Rabbah 2 calculates that they were twins and married Yaakov at 22.
I don’t follow the math, myself. It seems to just throw out there that Rachel was 36 when she died; since Yaakov married her after 7 years working for Lavan, and he left Charan after another 7 years after they got married, plus 6 years after all but Binyamin were born, and Rachel died at the end of the two-year journey back to Yitzchak, they were married for 15 years (I guess she wasn’t exactly 36 when she died).