Mid 30s, yes. Late 30s it would get more questionable.
Plenty of guys with less athleticism than Ohtani have played OF into their late 30s and 40s.
But anyways, you’re assuming worst-case scenario like you usually do when it comes to the Jays. Ohtani could likely morph into a hybrid DH/RP or OF/RP if it’s proven he’s no longer an effective SP.