Hi, Nancy -- My understanding is that babies are expected to double their weight by six months and triple their weight in a year, even if they were premature.  By those standards, this child is still ahead on growth.  My own son was born at 3#4", weighed in at 6#8" at six mos., and 13#6" at a year.  I was told you don't expect premies to catch up in the first year, that they achieve balance with the rest of the world by the end of the second year.

They do look a little eerie, walking and talking at 13#6", however.  And 
remember, their heads might still be "misshapen",  with the big part still 
behind their heads, depending on how premature they were,.  If I remember 
correctly. it's because the brain hasn't completely made the last fold yet.
They also  can tend to look slightly bulgy-eyed.

That he is alert and otherwise age-appropriate is reassuring.  My main
 concern would be with the short feedings, and the apparent changes in 
the way he feeds.    

You say that baby nurses only five minutes per feed?  How often are the 
feedings?  Karin Cadwell talks about an African culture that feeds a few 
minutes every 15 - 20 minutes, all day long.  But studies show that 
whether infants nurse on demand, on schedule, frequently or infrequently, 
at the end of 24 hours, the amount of nutritive sucking per day is the same, in terms of total minutes of suckling.

 My approach to lengthen the feedings would be:

If the baby nurses frequently, like every one to 1-1/2 hours:
Nurse the baby ea. side -- if only five minutes, then repeat ea. side.  After
 that repeat again, with an SNS in place.if.  If baby won't nurse the second 
time, use the SNS then.  This serves two purposes:  It lengthens the time 
at the breast, encouraging increased milk supply; and if baby was 
stopping because of no more milk, he will NOW nurse longer to get what's
coming from the supplementer. Remember, nursing two sides on one 
breast is what we suggest to moms who have an oversupply, to help cut
back.  Also, the breastfeeding both sides twice increases the fat content 
of the baby's feeding.  (It may also help the baby sleep a little longer until the next feed).

If it does turn out to be a case of low milk quantities, perhaps use of a galactagogue as well, pharmaceutical or herbal?

If feeds are infrequent (4 or more hours apart): start waking baby at 2-
1/2 hours, playing with him (her?) and encouraging feeding cues by 
playing mouth games, dolls eyes, sucking games, facial mimicking, and
then put him to breast, with supplementer right from the start.  Then pump 
after the feedings, ten minutes ea. side.  I tend to doubt that feedings are 
that far apart, or baby wouldn't be gaining weight.

For the "weaker" suck, he might need to be evaluated by a speech 
therapist, or someone more versed in the actual physio-anatomic side of things.

Chanita, San Francisco