Before we get to the answer, some housekeeping.
God can and does give grace to men in answer to their internal aspirations and prayers without the use of any external sign or ceremony. This will always be possible, because God, grace, and the soul are spiritual beings. God is not restricted to the use of material, visible symbols in dealing with men; the sacraments are not necessary in the sense that they could not have been dispensed with. But, if it is known that God has appointed external, visible ceremonies as the means by which certain graces are to be conferred on men, then in order to obtain those graces it will be necessary for men to make use of those Divinely appointed means.
A Sacrament, is an [b:2opwkv00]outward sign [/b:2opwkv00]of an [b:2opwkv00]inward Grace[/b:2opwkv00], [b:2opwkv00]Insituted by Christ[/b:2opwkv00] for our salvation. Some of the Sacraments were prefigured by rites preformed by the Jews in the Old Testament. In the case of the Baptism of John, first Jesus did not need baptism, because He was and is sinless. Secondly in the Scriptures we read in Acts I verse 5 [i:2opwkv00]”For John indeed baptized with water, but you shall be baptized with the Holy Ghost, not many days hence.” [/i:2opwkv00] John’s baptism was not Trinitarian, (in the Name of the Father and the Son and the Holy Spirit) as the concept of the Trinity had not yet been revealed by Jesus when he baptized Jesus. So while Jesus sets an example for us, it is not by being baptized by the Sacrament that He would soon institute.
The second question is inferred by the passages which speak of those who received baptism in Jail etc, and has been the constant teaching of the Church from the time of the Apostles. I’ll look up the actual verses soon, but in the mean time, here is a long article from the CE