The problem is that it's going to take a little bit longer before Michael stops looking like Evil Linus Van Pelt and gets the signature waviness to his hair that we associate with teenaged and adult Michael. This does not happen definitively for another four years or so. By then, Liz starts wearing glasses and switches to her 'four and a half foot tall girl with high ponytail' self. The sad thing is that by then, Mike starts getting all hormonal and strident about how awful it is that he deal with very mild restrictions on his behaviour. Sure, he started out as a stupid child who confused having to do what he's told with being hated but by the time he starts looking like his own person, he thinks that having to set a table when he wants to sit on his ass watching the box is torture or something.
This new Mike is also the same idiot Michael who couldn't get it through his thick skull that Martha wasn't playing politics with him when he didn't get what he wanted and the one who wailed idiotically about Rhetta crushing his heart in her machine because she didn't see the point of sitting on folded hands waiting for him to graduate from Uni. While he experimented with facial hair in order to antagonize Elly, it's pretty much a foregone conclusion that Mike's appearance freezes in place when he turns thirteen. It's also a foregone conclusion that having his head up his ass is a constant throughout his life.