X181a1 X1248 X3607 X151a X151b Group
1      18     0     1     0     0 Young
2      11     0     0     0     0 Young
3      16     2     0     0     0 Young
4      31     2     0     2     1 Young
5      44     0     0     0     0 Young
6      11     0     0     1     0 Young
7      11     3     0     0     0 Young
8      35     0     0     2     1 Young
9       6     4     0     0     0 Young
10     27     0     0     2     1 Young
11     19     0     0     0     0 Young
12     35     1     0     0     1   Old
13     17     4     0     0     0   Old
14     19     0     1     0     0   Old
15     24     3     0     0     0   Old
16     15     0     1     2     0   Old
17     30     0     0     0     0   Old
18     30     3     3     0     0   Old
19     17     1     0     0     0   Old
20     42     0     1     0     0   Old
21     37     6     5     0     0   Old
22     31    55     3     0     0   Old

There are significant differences in counts ("hits") between young and old for 181a-1, 1248, and 3607.

181a-1:

            Estimate Std. Error z value Pr(>|z|)
(Intercept)    3.036    0.06608  45.942  0.00000
GroupOld       0.260    0.08794   2.957  0.00311

1248:

             Estimate Std. Error   z value      Pr(>|z|)
(Intercept) 4.070e-15     0.3015 1.350e-14 1.00000000000
GroupOld    1.893e+00     0.3234 5.852e+00 0.00000000487

3607:

            Estimate Std. Error z value Pr(>|z|)
(Intercept)   -2.398      1.000  -2.398  0.01649
GroupOld       2.639      1.035   2.550  0.01079

151a:

            Estimate Std. Error z value Pr(>|z|)
(Intercept)   -0.452     0.3780  -1.196   0.2318
GroupOld      -1.253     0.8018  -1.562   0.1182

151b:

            Estimate Std. Error z value Pr(>|z|)
(Intercept)   -1.299     0.5774 -2.2504  0.02442
GroupOld      -1.099     1.1547 -0.9514  0.34139