title: Unable to install pandas=0.18.1 on Python3.6
body: <p>I am trying to setup a legacy project using python 3.6.13 as a constraint. Though I am running into an issue trying to install pandas version 0.18.1</p>
  <p>The log are as below:</p>
  <pre><code>Collecting numpy==1.11.1 (from -r requirements-remote.txt (line 25))
  Using cached https://files.pythonhosted.org/packages/e0/4c/515d7c4ac424ff38cc919f7099bf293dd064ba9a600e1e3835b3edefdb18/numpy-1.11.1.tar.gz
  Collecting pandas==0.18.1 (from -r requirements-remote.txt (line 26))
  Using cached https://files.pythonhosted.org/packages/11/09/e66eb844daba8680ddff26335d5b4fead77f60f957678243549a8dd4830d/pandas-0.18.1.tar.gz
  Complete output from command python setup.py egg_info:
  Traceback (most recent call last):
    File &quot;/Users/qqqqq/.pyenv/versions/3.6.13/envs/pyenv36/lib/python3.6/site-packages/setuptools/sandbox.py&quot;, line 154, in save_modules
      yield saved
    File &quot;/Users/qqqqq/.pyenv/versions/3.6.13/envs/pyenv36/lib/python3.6/site-packages/setuptools/sandbox.py&quot;, line 195, in setup_context
      yield
    File &quot;/Users/qqqqq/.pyenv/versions/3.6.13/envs/pyenv36/lib/python3.6/site-packages/setuptools/sandbox.py&quot;, line 250, in run_setup
      _execfile(setup_script, ns)
    File &quot;/Users/qqqqq/.pyenv/versions/3.6.13/envs/pyenv36/lib/python3.6/site-packages/setuptools/sandbox.py&quot;, line 45, in _execfile
      exec(code, globals, locals)
    File &quot;/var/folders/zc/tjmjl2890y57f30n1yg7dg39xl_6k6/T/easy_install-zcqg452m/numpy-1.21.0rc2/setup.py&quot;, line 34, in &lt;module&gt;
      _CYTHON_INSTALLED = ver &gt;= LooseVersion(min_cython_ver)
  RuntimeError: Python version &gt;= 3.7 required.
  </code></pre>