I mean if the guy probably hasn't really done any rigorous exercise since high school. Especially since he was so busy with either uni or finding a job, there wasn't any time for him to actually keep track of his body when it was required back in his hometown and high school. While yes it was a little exaggerated, 10 year is quite a long time to see that his body isn't used to doing rigorous activities. So it's not as left field as you think?? And also as Yoake said, he'll get used to it and his body will come back in shape within the year.
Also he's not crippled as he pulled a muscle (since he didn't warm up beforehand) and he tripped (which is normal) but since inside is still 27 years old, his regeneration is not as great as a kid. He can still walk of course and it probably isn't as serious (but Asaji wants to carry the guy so um.. it turned into a ruckus when in actuality, it probably isn't as serious as it is)