The Bible doesn't forbid people from marrying each other just because they are different in age. Abraham, for example, was 10 years older than his wife Sarah (see Genesis 17:17), and some Bible scholars have suggested that Joseph was probably several years older than Mary (since he apparently had died by the time Jesus' ministry began).
At the same time, I hope you will listen to your mother with an open mind, because she may have reasons for her concern that you need to consider. I can probably guess some of the questions she is asking: What do you really know about this person? Has he been married before -- and if so, why did the marriage end? What kind of husband and father will he make? Are there other things in his background that ought to cause you concern?
However, the real question you should be asking yourself is this: Is it God's will for me to continue with this relationship? To put it another way, are you honestly seeking God's will for your life -- including your marriage?
If not, the most important step you can take is to turn to Christ and invite Him into your life. Then ask Him to make His will about this relationship clear to you. Let the psalmist's prayer become yours: "Teach me to do your will, for you are my God; may your good Spirit lead me on level ground" (Psalm 143:10).