aluminium fatigue how to know if some thing is going wrong?
I have a 1998 aluminium road bike, and it made creaking noises in the stem when pedaling hard.  Could replicate this by siezing the bars while stopped and wiggling.  So I tightened the quill stem and the noise went away.  Its just a bit of play in the steerer tube/quill stem fixing.

Since you're asking, a frame should outlive you, assuming no crash damage and its garaged/treated well.

Give it a good wash and then look over the frame for any cracks... but try and see if they're paint cracks or frame cracks. 

Then run your bare fingers over the surfaces - you should feel only flatness, no ripples or bends.

Your bike is probably welded, not lugged, so have a close look at the welds.  Ideally they should be smooth and flat, but some bike welds look like beginners (cheaper MTBs are chronic for the industrial weld look)

Forks can be measured to make sure they're not bent too, but this is fiddly and normally only done if the bike doesn't track right, or there was a frontal impact.