If you have other federal loans (such as FFEL, Parent PLUS, or Perkins loans), you can consolidate them into a Direct Consolidation Loan which qualify. The one exception is FFEL Joint/Spousal Consolidation loans, this can be consolidated by through a different process here: https://bysavi.zendesk.com/hc/en-us/articles/1500007391481-What-s-the-deal-with-Joint-Spousal-Consolidation-Loans
As for how it affects PSLF, according to Federal Student Aid Office, you will receive a weighted average of qualifying payments on your Direct Consolidation Loan to be counted toward the 120 payments required for the program.
In order to consolidate your loans into a qualifying Direct Consolidation Loan, you may submit a consolidation application online after logging in to your Federal Student Aid account at studentaid.gov.
Read more about Direct Consolidation Loans: https://bysavi.zendesk.com/hc/en-us/articles/16168129717267-Overview-of-Consolidation