The OP was a little vague - no insight as to how often he works out. Yes, you do need some stamina to play golf for a variety of reasons. What is the weather like when he plays? Very hot and humid? If he's tired after 7-8 holes and the performance is suffering, then, yes, I'd say we may have a stamina issue.
It's nice that you are 48 and have plenty of stamina, but that in no way offers any real guidance here. For all we know this guy is woefully out of shape with bad a bad diet to boot (stating this for argument's sake - not implying that just because he has low stamina, he's overweight and possesses bad eating habits).
Amjad -
Some more questions. Do you your normally walk or ride? If you walk, can you use a push cart? I have found that when I use a push cart and I take a few less practice swings, I am a little less tired.
If you want to increase some stamina, I suggest some HIIT training as John suggests AND some moderate cardiovascular activity at long(er) periods of time. This can be anything you want - light jogging, walking, biking, etc - but the pace and intensity is moderate. On a 1 to 10 scale (10 being all out effort), moderate is basically a 5 or 6. Go for a nice hike for an hour and while doing so, you should be able to carry on a conversation. If you are totally winded, you may be working too hard (or maybe really out of shape).
If you play in hot weather, it goes without saying that hydration is important. Carry some fruit and nuts with you for a snack every 3-4 holes.
As far as power goes, well there are a few ways to go about that. If you want to actually swing faster, it helps to swing light objects quickly. Learn to develop the speed and swing fast(er) than you are now. Remember that the golf swing involves gradual acceleration and all too often high handicappers expend their energy way too early. You really don't need a very high swing speed to hit the ball very far. Maybe 90 mph driver swing with a solid strike to the sweet spot will result in a 235 yard drive - good enough for most people on most courses.