Though he is seven years old ,he can manage_____(do)everthing by himself.

to do
manage to
达成, 设法

参考例句
He managed to skip the washing - up.
他变著法地不做洗碗的事。
Xiao Lin managed to accomplish her work in time.
小林设法及时完成了任务。
She just managed to hold back her anger.
她总算抑制住了自己的愤怒情绪.
Our car just managed to clear the truck.
我们的汽车成功地越过货车。
He managed to subdue his mounting anger.
他设法克制住了阵阵愤怒。
He managed to finish his job with difficulty.
他费力地完成他的工作。
He managed to endear himself to everybody.
他有办法让大家都喜欢他.
I wish very much you could manage to come over.
我非常希望你能来。

to do
虽然他只有7岁，但什么都能自己打理。

manage to do sth 成功做某事

manage to do sth成功做某事
尽管他7岁，但他可以自己成功解决每件事了
也可以用succeed in doing

to do
manage to do努力完成的意思。

to do
设法成功地做某事

就是to do 吧 。。