code: func (st *Store) MaxAge(age int) {
  	st.SessionOpts.MaxAge = age
  	for _, codec := range st.Codecs {
  		if sc, ok := codec.(*securecookie.SecureCookie); ok {
  			sc.MaxAge(age)
  		}
  	}
  }
docs: // MaxAge sets the maximum age for the store and the underlying cookie
  // implementation. Individual sessions can be deleted by setting
  // Options.MaxAge = -1 for that session.