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Mobile payment (Alipay and WeChat Pay) has gradually become a payment method for people's shopping consumption. To investigate the age structure of citizens using mobile payment, a random survey of 100 citizens was conducted, and a $2\times 2$ contingency table was obtained as follows:

|                  | 35 years old and below (including 35 years old) | Above 35 years old | Total |
|------------------|--------------------------------------------------|--------------------|-------|
| Using mobile payment | 40                                               |                    | 50    |
| Not using mobile payment |                                                  | 40                 |       |
| Total            |                                                  |                    | 100   |

$(1)$ Complete the above $2\times 2$ contingency table and by calculation, determine whether there is a $99.9\%$ certainty that the payment method is related to age.  
$(2)$ In the group of people using mobile payment, $10$ people were further sampled using stratified sampling. From these $10$ people, $2$ people were randomly selected. Let $X$ be the number of people under the age of 35 (including 35 years old) among these $2$ people. Find the distribution of $X$ and its expectation.  
Reference formula: $K^{2}=\frac{{n{{(ad-bc)}^2}}}{{(a+b)(c+d)(a+c)(b+d)}}$, where $n=a+b+c+d$.  
Reference critical value table:

| $P(K^{2}\geqslant k)$ | 0.5  | 0.4  | 0.25 | 0.15 | 0.10 | 0.05 | 0.025 | 0.010 | 0.005 | 0.001 |
|-----------------------|------|------|------|------|------|------|-------|-------|-------|-------|
| $k$                   | 0.455| 0.708| 1.323| 2.072| 2.706| 3.841| 5.024 | 6.635 | 7.879 | 10.828|

Present the answer in LaTex format: \boxed{Your answer}
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