Are my previous prayers invalid due to my ignorance of the place of intention in wudu, and am I correct now when I make the intention with washing the face?

Your ablution is valid, and there is nothing against you. The jurists have mentioned the obligation of having the intention at the beginning of the first obligatory acts of purification, and this does not mean that if one made the intention before the first obligatory acts, their ablution would not be valid. Rather, they explicitly stated that making the intention when washing the hands at the beginning of ablution is a Sunnah (definition), as stated in "Al-Rawd Al-Murbi'."