to get by/along;  to contrive;  to swing;  to shift for oneself;  to look after oneself;  to take care of oneself;  to fend for oneself;  to manage (on one's own/by oneself)
He'll have to manage (by himself)!;  He'll have to sort it out for himself!
Don't worry, I'll manage somehow!
He's old enough to look after himself!;  He's old enough to fend for himself!
Up-and-coming;  resourceful