Although he's nearly 80,he is still very active.=He is still very active,although he's nearly 80.尽管快80岁了,他还是十分活跃.although不与but连用
although能作为连词链接两个简单句形成并列句
Although he's nearly 80,he is still very active.=He is still very active,although he's nearly 80.尽管快80岁了,他还是十分活跃.although不与but连用