@alx. Yes, the Spanish is clearly saying that is "your father, the one who feels old, just because he is 70 years old".
I don't know exactly how to put in in correct English, I'll give it a couple of tries, but the English natives can re-touch it or re-write it altogether!
Don't go the way your father went,
who feels old just because he is 70 years old,
Or,
Don't fall for what your father fell for,
who [your father] feels old just because he is 70 years old,
The father adopted an attitude, or swallowed some kind of myth about "being young/old" and believed and that's why now
he feels old, when as a matter of fact he is just a little 70 years old kid!
Note: Didn't see Irmamar post after I wrote my post, so the "Yes" is addressed to Alx...