Can you live a normal active life with spondylosis? like triathlons and other activities?

Absolutely!: So long as you have no loss of function of any muscles, your bowel, or your bladder. Your body will usually stabilize everything (if it hasn't already) by making the ligaments bigger/thicker. Staying active is the best way to prevent progression and keep the supporting muscles strong. Just activities that reproduce your back pain.

Arthritis: Spondylosis refers to arthritis of the spine due to wear and tear and afflicts many people. Your activity capabilities depend on the extent of loss of flexibility and degree of pain which would put limits on your performance. This is different from spondylitis which is a more inflammatory process requiring more aggressive therapy and usually limits activities much more severely and is rarer.