The same way you'd get involved if you were 18 or 40. Your age doesn't matter, so long as you are old enough to actually join the site. Take a look at the Roleplay Requests for Females, Roleplay Requests for Males, or Roleplay Requests for Uncategorized Others sections to find a one on one role-play. If you want a group roleplay, then take a look at System Styles Roleplays, Group Roleplays, and Open Roleplays. When you find what you like, contact the person that owns the thread by following their rules (either clearly listed, or hidden in walls of text). If they don't have rules for contact, then either post in the thread or send the owner of the thread a PM. Use your best judgement and preferences on how to make contact.