All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
You must fulfill whatever you remember of those vows, because the Prophet said: “Whoever vows to obey Allah, let him obey Him.” [Al-Bukhari]
If you had vowed to perform a prayer, you must perform it, and if you had vowed to fast, you must fast, and likewise if you had vowed to give charity, you must give charity whether this vow is conditional or not.
As for the vow of Lijaaj (a vow made in order to prevent oneself from something), then you have the choice between fulfilling it or paying an expiation for breaking it.
You are not exempted from the fulfillment of the vow of obedience because of the passage of time. Rather, you must fulfill it in any case, unless you forgot the vow or were unable to fulfill it and this inability is not hoped that it will be removed.
Regarding the oaths that you had forgotten, it is enough to expiate once for breaking a vow as this is what you are able to do, and Allah does not burden a soul beyond its capacity.
You should try to estimate the number of these vows and expiate for a number that you think would most likely clear yourself of liability. According to the Hanbali School it is sufficient to expiate once for all the vows that you had forgotten or that you could not fulfill.
For more benefit on breaking an oath and expiating for it, please refer to Fatawa 367117, 356647, 102811, 138168, 96130, 311782, 136842 and 252961.
For more benefit on Lijaaj vow (a vow made in order to prevent oneself from something), please refer to Fatawa 374149 and 446746.
Allah Knows best.