A319 First Officer reported a fume event during descent. Maintenance met the aircraft at arrival gate and began troubleshooting.

Narrative

During Cruise; started noticing a faint crayon like smell. I closed all my vents and smell dissipated. Mentioned smell to Captain; but he didn't notice anything. During descent when the thrust reduced for idle; the smell came back stronger. During which time; I notified the Captain; 'there's the smell.' The Captain noticed it and mentioned it smelled like paraffin wax. Captain called the cabin who noted they smelled a musty smell; but nothing that they had ever smelled before and couldn't pin point the smell.Upon gate arrival; we were met by a MX (Maintenance) Manager who we explained the issue to. He didn't smell it at the time of explanation; but the APU bleed was off to prevent further contamination while deplaning. After all crew (except pilots) and passengers were off; the APU bleed was turned on. During this time; the smell was apparent and all four MX personnel and Manager noticed the issue. The MX manager mentioned that the airframe just had its 4th heavy check; which are due every 12 years. With the plethora of speed tape on the exterior; paint chipping; lack of engine synchronization during power up; and overall rattles during taxi; take-off; and landing; I'd say the airframe is near the end of useful life.The [issue is] companies insistence on keeping this airframe flying even though it's past its useful life. Also; lack of staffing and parts enabling consistent well rule aircraft.Suggestions [are to] retire Aircraft XXX and similar aircraft that are consistently having these fume events. This is the 3rd event in 6 months on an older Airbus. Either MX is failing at properly following SOP and work cards; or there's a push to get aircraft back in the air due to demand by management skipping important safety checks!