Have a ticking noise coming from inside engine,mechanic thinks its probably a worn canshaft 170000kms

When a camshaft wears it is usually one or more cam lobes that are affected and as it is the peak of the lobe that does most of the work of opening the valves that is typically where most of the wear takes place so instead of a smooth curve that glides silently across the cam follower or tappet a worn cam lobe tends to develop a rather square-ish profile and the sharper edge "hits" the cam follower resulting in a ticking noise.

This sort of wear has a distinctive noise characteristic in that as the engine speed is raised from idle the noise becomes more defined and louder because the squarer edge is hitting the cam follower harder.
When other parts of the valve gear are worn the noises at idle speed tend to fade as the speed is increased.

The cause of this sort of wear is usually lubrication-related. On older engines that are dirty inside it is often a small oilway that becomes blocked. It is important to discover the cause before spending lots of money on a new camshaft and related parts in case it is wasted by the same fault recurring.
Other causes are insufficient oil changes, poor quality engine oil, low oil pressure, lots of cold starts and driving away too soon after starting.

It is worth noting the swarf from the worn cam lobe(s), the finely powdered metal, will have been washed down into the oil pan or sump where there is a good chance they have been picked up and travelled around the oil pump before being trapped in the oil filter resulting in an oil pump slightly (or a lot) more worn and less efficient than it should be.
While in many cases this would not be a great problem, for engines that travel only lots of short distances the resulting oil drain-back and an extra second or two to reach maximum oil pressure after starting can have a negative affect on the life of an engine and a new camshaft.

The noise is most likely from worn hydraulic lifters rather than cam shaft
the key is your statement that the noise is worse when starting up
Cam shaft noise will be constant with rpms but lifter noise will decrease as the oil pressure builds up
At the klms you state , it is time for a hydraulic lifters set to be removed and have a leak down test done as they will be showing signs of wear
Find an accredited service shop that specializes in your make of car , have the noise properly diagnosed and get a quote for repairs