八十多岁的老父母 都有绿卡很多年。今年底想回中国。 我现在想着手办理回美证：
1）是到哪里下载131 ， 还是必须打印出来 ， 父母分别填好 ，寄给移民局吗？
-Yes, they only can file the application by mail, not online. Check this link:
Application for Travel Documents, Parole Documents, and Arrival/Departure Records | USCIS
2） 寄出去以后，拿不到回美证也可以回国吗？
-Yes. Your parents can leave US after they receive the I-131 receipt notice. Because they are more than 79 years old, they don't need to do the biometrics, but need to provide two their passport style photographs with the I-131 filing.
等回美证寄过来再给他们送到中国？
-Yes; or ask USCIS to send it to the US Consulate in China and then, they can pick it up at the US Consulate (you need to indicate it in the I-131 if they want to pick it up at the US Consulate).
谢谢八老师的帮助。
