If I do not make a bone graft after extraction, am I able to have an implant later?

The answer is yes- You can always have an implant later. The only question is whether there is sufficient bone for implant placement. If not, then bone grafting will be necessary. Generally, I recommend to graft the extraction site if there is already bone missing or the implant is planned beyond 3 months following tooth extraction.  The link below will expand on this topic more.

It is more ideal to have bone grafting done at the time of extraction than it is to go back later and bone graft. This is not to say that it can't be done. technology is constantly changing and progressing so you may still be able to have an implant placed later, it may just require more time, effort and cost.

This is a great question.  A bone graft will give you a better chance in the future to receive a dental implant.  There is no way to know for sure how your bone will resorb after the extraction - the more bone you have after the tooth is removed, the better your chance is.  Once the tooth is gone, there is no need for the bone and it often starts to resorb rather quickly.  Generally, there is a 25% decrease in width of bone during the first year, after tooth loss and an overall decrease in height over the next few years. Over time 65% of the bone resorbs, If no measure is taken to preserve the bone.