How to calculate aging tolerance of Resistor?
According to the datasheet, the test is done in compliance with MIL-STD-202, method 108 (pp 37-38), condition D (1,000h). 

This is an accelerated aging test at (probably) 100% rated power (while "ON") with a duty cycle of 75%. Your operating conditions will almost certainly be more benvolent than these, which in practice means that the stress of your resistor may be lower than the usual assumption.

We know from Arrhenius that each additional 10°C accelerates reactions by an aging factor \$Q_{10}\$, that is:

$$
\frac{t_0}{t_{acc}}=Q_{10}^{\frac{T_{acc}-T_0}{10}}
$$

From that, we can calculate that those 1,000h operating at 100% rated power at 70°C are roughly equivalent (i.e. induce the same aging-related drift) to 31 months (2.583 years) at 100% rated power at 25°C, assuming the usual aging factor \$Q_{10}=2\$.

That amounts to 1% over 2.583 years or an average 3,870 ppm/year at 25°C. You can recalculate this for any operating temperature by using the equation above. Note: this is probably a conservative calculation due to operating conditions.

However, the aging drift does not increase linearly with time, but rather with the square root of time:

$$
\frac{\Delta R}{R}=K\sqrt{t}
$$

Recall that the previous calculation of 3,870 ppm/year was an average for the 2.583 years of the calculation period, but the actual implicit aging constant at 25°C is K=6,225 \$ppm/\sqrt{year}\$, which is a better case. Note that the aging drift are stronger during the first years, and smoother (slower) afterwards:


2.583 years: 10,000 pmm (1,0%) as specified
5 years: 13,919 ppm (1,4%)
10 years: 19,685 ppm (2,0%)
20 years: 27,839 ppm (2,8%)
40 years: 39,370 ppm (3,9%)