Replace `start` with `ticket_creation`

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_ticket.c b/library/ssl_ticket.c
index c89a5cd..05249ea 100644
--- a/library/ssl_ticket.c
+++ b/library/ssl_ticket.c
@@ -498,16 +498,17 @@
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
     if (session->tls_version == MBEDTLS_SSL_VERSION_TLS1_3) {
         /* Check for expiration */
-        mbedtls_ms_time_t ticket_age = mbedtls_ms_time() - session->start;
+        mbedtls_ms_time_t ticket_age = mbedtls_ms_time() - session->ticket_creation;
         mbedtls_ms_time_t ticket_lifetime = ctx->ticket_lifetime * 1000;
 
         if (ticket_age < 0 || ticket_age > ticket_lifetime) {
             ret = MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED;
             goto cleanup;
         }
-    } else
+    }
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
-    {
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+    if (session->tls_version == MBEDTLS_SSL_VERSION_TLS1_2) {
         /* Check for expiration */
         mbedtls_time_t current_time = mbedtls_time(NULL);
 
@@ -517,6 +518,7 @@
             goto cleanup;
         }
     }
+#endif
 #endif /* MBEDTLS_HAVE_TIME */
 
 cleanup: