The missing person poster lists Mike's age as 26. Zoe Sharp, the first victim, was Mike's birth mother, who had died 20 years earlier (according to Captain Connors) while Mike was still a baby (according to Mike's girlfriend). This would make Mike only 20 years old, 21 at the most.
In the final scene, when Henry is looking at Brett's commendation, he has his thumb over the first word in front of Brett Conners' name. This word ends with a 'T'. When Conners takes the award back, it can be seen that it is made out to "Sergeant Brett Conners (RET)." Conners retired as a Captain, not a Sergeant.
When Sabrina comments about how Mike's whole life can be summed up with a box full of items, she mouths something else.
In the newspaper article about Mike his last name is McKay, but later when we meet Mike's girlfriend she has a box holding Mike's personal belongings and it is labeled McMillan, M. indicating that Mike's last name is McMillan.
When Shawn is talking to the Zoo director about Dr. mcTook's language, he pronounces Xhosa as "kho-sa" when, in actuality, it is pronounced more like *click*-owsah"