Totally normal. Not a speech therapist, but I am a school psychologist and early childhood specialist. From a developmental standpoint, though, the "adjusted age" thing doesn't really mean much with respect to language development. Unless you child has a neurologically-based language disorder (doesn't sound like it), language is learned through exposure and interpersonal interactions. The premature birth tends to impact more notably in the area of physical development and motor control.
If your son doesn't hit the "language explosion" around age 2, then bring it up to your pediatrician. Otherwise, all children develop language at drastically different rates. Boys tend to develop language more slowly, but may mature with respect to motor skills more rapidly. The "benchmark" is really taken at age 2, but not of concern (requiring an assessment) until closer to 30 months.
Encourage him to use words by "forcing" him to use them. If he point, make him say the word (even if it doesn't sound like the item) in order to obtain the item. You, as mommy, will often predict what he wants and get it ahead of time (think water or juice with a meal b/c you know that's what he likes), but have him ask for it!
We also taught my son simple sign language starting at this age to reduce his frustration and increase his communication. He's 4.5 now and still signs (along with talking) "please", "thank you", "more" and some of the others he knows.
No worries, mommy. He's doing just fine!