Dating Picture From Type Of Photo?

I'm trying to date this picture and was wondering if the process that was used to produce it can somehow date it.
I've also noticed this type or process was used on some postcards, Birthday cards etc.. When tilted in the light some areas of the picture changes to a bright blue.
The item below is a picture I bought at a flea market thinking it looked a lot like a older Alexander Graham Bell. (Bell Died in 1922)
With the photo being of this type could it aid in dating it?

Cheers, Bill

I don't' actually know the answer to your question but it's a very attractive picture!

I know absolutely nothing about dating photographs. If it were mine, I would take the picture out of the frame and check for any markings on the back - photographer, date, notations etc.

Dan

Generally, clothing, shoes and furniture can give clues, but I don't see much here that helps. I think Dan's suggestion is very good.

Late 20's early 30s due tyle of print, bull-nose treads, hat plus shoes and posing method. That said look at the back as suggested above.

The framing and matting is more recent.

Thanks to everyone I appreciate all the assistance so far.
Well here's a picture of the back and a closer picture of the frame.
The picture it adhered to the matting so you can't see the back of the actual picture but on the back of the matting it reads 394 FO or FQ.
The outside viewed from the back when assembled has the number 394 repeated again but without the FO or FQ.

Cheers, Bill

This type of mottling on old photographic prints is usually caused by poor quality processing. The final steps in processing a print are to fix the developed print using Sodium Thiosulfate to remove any residual silver halide in the emulsion that has not been converted to metallic silver in the development step. If the print is not properly fixed, over time the silver will start to discolour like this as it is exposed to light.

My guess is that the original image was made in the 1910s or early 20s.

The first photo in the original post and the last partial photo above do not show the mottling. The ones that do are due to the flash except for the reversal (negative) image done by an app.