To be honest, I don't think that's proportionate.
It's a sad story, but all he did was snatch a purse and shove her over. If she hadn't landed badly then this would barely have made the local rag, let alone make waves in the pages of GD.
Can't imagine causing anything beyond minor injury (cuts/bruises) would have been in mind when committing the act.
He should do time, of course, but let's not get silly.
I think it is entirely proportionate.
If you brutally assault somebody who is clearly extremely elderly and frail then it is highly likely that serious life changing injury and/or death is an almost inevitable outcome.
The "I didn't mean to do it" defense may have some technical justification but the sentence should reflect the fact that the perp was completely reckless as to the serious injuries or death that he would almost certainly cause.
One would not get away with "Accidentally" killing somebody in a drive by shooting on the basis that you didn't mean to, and under these circumstances this perp shouldn't get away with it either.
Personally I am all for the "Felony Murder" doctrine, then we wouldn't be having this debate.