What is the best age to get married to be saved from fitnahs? And is it permissible to marry a girl older than me? What kind of evidence or proves can I give to strong my case in terms of age?

There is no specific age for marriage for a man, so if you fear that you will fall into the forbidden, whether this forbidden is looking at women with lust, or masturbation, then you must marry.
With regard to the second question, It is permissible to marry someone who is older than you, and there is no objection to that.