Don't worry about why he's with you or how long he'll stay. Both are beyond your scope of responsibility. Those are *HIS* areas. Work on you and *YOUR* areas. Clingy and codependent do NOT make a good relationship, regardless of the other partner's age. There are literally thousands of books out there on the matter, and therapists and counselors galore very capable of helping guide you. But, only YOU can break the habits, only YOU can change your attitudes, actions, etc.
I've been involved with men not quite young enough to be my kids (that would just be too weird for me personally) to men twice my age. Previously, I'd married men about my age or older. My husband and absolute love of my life is about 5 years younger than me and definitely more mature than they were. Physical age is relative. Emotional maturity is at least if not more important. Maybe you're attracted to him because you feel less emotionally mature than your age?
Learn boundaries; where you and your responsibilities end and where other people's begin. Your happiness and satisfaction are YOUR responsibility, not your partner's, not your parents', not your boss's, not your analyst's, not your doctor's - YOURS. If you are unhappy with the way things are now, work to change them, especially if you are unhappy with *you*.
Life is full of decisions, choices, actions, and consequences. Learn to respond to situations and people, not react to them. Take back control over yourself and drop trying to control anyone else. We tend to try to fix, control, or manipulate other people to try to get them to do things the way *we* want, as a way of avoiding focusing on ourselves. Work on finding out who you are, and you'll quit needing someone else to tell you. Work on being someone you like and respect and you won't need to have other people's approval. Learn to like and love yourself and you won't *need* it from outside sources. Learn to stand on your own and you won't need to cling or lean on anyone else.
Love is not a hostage situation. Love is being together because you *want* to share, not because you *need* each other. Love is both giving 100% because you want to, not because you expect anything in return. This doesn't mean one gives and the other takes. Love is open hands and open hearts, sharing and caring, not clinging and needing. Love is not fearful. Love is the opposite of fear.