Wouldn't Shrek and Fiona be old? He already looked like he was aging in the first few movies. I think it's because of the general style of the models. And now with his children, from what I assume, are either teenagers or grown, both him and Fiona would have visible facial aging at this point. I think that's a bigger disappointment than the fact they look like, as everyone else's saying, something you'd see from AI content farms.
He looks like he hasn't aged a day. The old style of him really complimented his age the best.