I think that boys of fourteen would have worn clothes like that of the younger children, as they wouldn't have been old enough yet to forget the "infantile breeches." That didn't happen until their sixteenth birthday, if they followed the typical Edwardian rules of fashion (which, by the way, included children up to the age of four or five still wearing pinafores). I would think, however, that they wouldn't wear the more childish sailor suit, but I may be mistaken. Here is an advertisement for boys' clothes around the time the Titanic sank.
Many of the clothing styles are found by Image searching the name in Google if you want a visual. Most of the clothes are also universal in age, where a boy wears the same style as their father, grandfather, etc., etc. Hope this helps.
Here's a pic of an upper class English father and son casually dressed in matching style, around 1910. The boy might be 16 but is probably a little younger; the transition from knee breeches to long trousers often came earlier at this level of society, where new clothes could be afforded more frequently. It would be quite normal, however, for both father and son to be wearing knee breeches when dressed for walking or some other outdoor activity.
Working class males on the Titanic would be in their Sunday best - very similar in general cut (but not quality) to the causal wear of the toffs, but almost always in dark colours which made their one suit more versatile. And a working class lad of 14 would almost certainly be in knee breeches and possibly also the large 'Eton collar' which was standard for boys of all classes.
In England, certainly. From the age of around 11 or 12 upper class boys attended boarding schools like Eton or Harrow, where the uniform included long trousers. At Eton the younger boys (see below) wore a short 'bum freezer' jacket, while the older boys wore a tail coat. And all wore top hats! The 'Eton suit' (minus the topper) became a fairly standard fashion for younger boys of the middle and upper classes.
Oh, I see. I understand very well. I have been working on my own story of the Titanic. What is your story about? I don't want to steal your ideas (I have plenty of my own) but I would like to know the general plot 'n stuff. I'll tell you mine if you tell me yours.