How many intoxicated manslaughter cases have resulted in 10 years probation in Tarrant County this year? Several. How many of those sentences were for adults? All but this one. How many were a minority? At least one.
Of all those people, how many had just stolen the alcohol they drank and were about to go steal some more? How many were also high on vallium? How many were going twice the legal speed limit? What was the average level of intoxication, was it 3x like in this case? I don't think his age is a call for leniency (in that I don't think his brain would be functioning any better at 18), if anything that's just yet another crime he's guilty of (underage drinking).
There's a big gap between minimum and maximum sentence because situations vary. I could think of DUI + vehicular manslaughter scenarios that might call for more lenience than this. I definitely don't think this qualifies for the minimum. No one's arguing that the judgement is illegal but that doesn't make it appropriate.
It really doesn't even matter whose fault it is that he ended up this way or why it happened. I bet you anything that this will only reinforce his feelings that he can get away with anything and I really doubt it'll stop him from screwing up again. Hopefully his probation will actually stick when that happens but who knows what the price will be.