If the panda is 26 years old, how old would that be in human age?
Roughly speaking, a panda who is 26 years would be how old as a human?
ご質問ありがとうございます。
① "If the panda is 26 years old,"＝「もしパンダが26歳だとしたら、」
"how old would that be in human age?"＝「それは人間で何歳になるのだろう？」
② "Roughly speaking,"＝「大体で、」
"a panda who is 26 years would be how old as a human?"＝「26歳のパンダは人間の何歳だろう？」
ご参考までに。
If a panda is twenty six years old, how old is that in human years?
How old is a twenty-six-year-old panda in human terms?
この場合、次のような聞き方ができます。
ーIf a panda is twenty six years old, how old is that in human years?
「もしパンダが26歳なら、人間の歳だと何歳？」
How old is that in human years? で「それは人間の年齢だと何歳？」
ーHow old is a twenty-six-year-old panda in human terms?
「26歳のパンダは人間だと何歳？」
How old is ... in human terms? で「…は人間だと何歳？」
ご参考まで！
アメリカ合衆国 
カナダ 
