Is swimming 148 lengths in a 25m pool in one hour good for a 13 year old?

If your question is whether it is good for the swimmers health, then no. That is the roughly swimming 2 miles in an hour, and swimming 61 yards each minute. I extremely advise you not to do this without guidance from a coach, and experience. This is something that an olympic distance swimmer would do in the Olympics.

If your question is if that is a good time for a 13 year old, then the answer is:

YES.

Please dont try this, I have hurt my shoulder from overuse while swimming, and it hurts. I had to sit out for 3 months, and still cant swim butterfly.