Many will look to the Eunuch and say he was immediately baptized.
I would probably would have done the same as - I believed he fully
understood what baptism was all about.
In this day and age, when people mention baptism, many will think about a baby being sprinkled.
I agree with Rlvaughn states that "It signifies a spiritual commitment, that we who are born again are now free to walk in newness of life"
But someone who has no previous Bible training will not fully understand the significance of that spiritual commitment
In addition - a young child - say 4-6 years old will not fully understand either - basically for the reason stated above.
On other thing - normally when a person is baptized - they are also joining the church.
So, Tom gets saved Sun am - baptized Sun Pm - joins the church on Wed PM
then a month or so later we find out that Tom believes in abortion, does not believe in the Trinity, thinks you can loose your salvation -
sees nothing wrong with boozing it up on Fri pm - as long as he is in church Sun AM..
This is my testimony - I was attending church faithfully for over 5 years - thinking I was born again - then in 1963, I came to the conclusion I was not. About a year later I talked to the pastor about being baptized. At our church, candidates would attend a 13 week class. I leaned a lot in those classes - and when i was baptized - it meant so much more to me. I then fully understood the significance of that spiritual commitment. (except at the time, I was not baptized with my wallet

) I would never exchange that experience for anything.
And likewise - I doubt I would ever baptize anyone younger that ten years old.