So, was Relias drinking, gambling, and whoring since he was a baby?

With time out for the other activities proper to pampered nobility in his father's court.  But the phrase, "X did nothing but write during the remainder of his life," or "Y focused entirely on ruling during 30 years on the throne," has never meant that's all they did. 

But if you say someone did something for x number of years, it's reasonable to assume they engaged in it regularly it at least once a year.  

Oh hell yeah I was a playboy at the age of three, man those ladies never stood a chance I wonder if it meant the last 24 years of his life, since it does not say how old Relias is and channelers always look younger than they are.

last 24 does actually make more sense.

Of course he's been drinking and whoring since he was a baby... think about why he sees all the colors and believes he does magic... It only makes sense....

I'm willing to bet that the average lifespan in the world of Elemental is at most 40.  Between horrible sanitary practices, close proximity of the few survivors, and the fact that there are horrible monsters literally waiting outside the walls to eat your brains, it's quite likely that Elemental's society is similar to that of the Dark Ages, when people would get married around 12-14 and then die at age 30ish from the plague.  Given that, it's entirely likely that he was drinking, gambling, and whoring as soon as puberty hit.

He was sucking on a teat from the day he was born!

perhaps his wet nurse was also a prostitute and a heavy drinker.  what's this game rated by the way?

I've been whoring and drinking since I was 7, but I don't gamble, I have my moral limits.