I wanted to say...

Hope this helps Joey,

"My parents are too old comparing with parents of my friends. They are about 20years older than my friends'."

A.  My parents are too old compared to my friend's parents; I think they are about 20 years older than my friends' .

OR

Compared to friends' parents, my parents are really old; they're just about 20 years older than they are.  

**( Than they are was highlighted blue and/or italicized because instead of reusing the same subjects/objects in a given expression try incorporating pronouns to avoid cases of redundancy in both spoken and written English )**

"I will have a lunch at a restaurant that I tried to go to several times but failed because of so many people in lunch time."

B.  I will have lunch at a restaurant that I tried to go to several times before, but I couldn't because there were so many people there at lunch time.

OR

I will have lunch at a restaurant that I tried to go to before, but I didn't because it was really packed during lunch hours. 

Peace,

Teacher Tristan