Do I absolutely need a lawyer for a fourth degree misdemeanor, if is my first time conviction of any crime and I'm at age 50?

Strictly speaking, no.  However, it is often said that he who represents himself has a fool for a client.  In a situation such as the one you describe, the purpose of hiring an experienced attorney is to help see to it that you are treated fairly under the law, that your rights are not being compromised without your knwledge and consent, that you are fully advised of those rights, and to help you try to minimize the effects of an unfavorable outcome or, if you are not guilty, to prevail in your behalf.