Could it be too late to fix periodontal disease?

Not too late: Please see your dentist, or the periodontist he/she recommends, for evaluation and treatment options. I commend you for wanting to get this problem under control.

Never too late: Treating periodontal disease in any stage can help prevent tooth loss and general health problems (e.g. cardiovascular).

Never too late: to get an evaluation. Periodontal disease takes many years to manifest itself, so hopefully at your age there's a chance for recovery. Make an appointment with a periodontist.